Media over QUIC Transport
draft-ietf-moq-transport-17
| Document | Type | Active Internet-Draft (moq WG) | |
|---|---|---|---|
| Authors | Suhas Nandakumar , Victor Vasiliev , Ian Swett , Alan Frindell | ||
| Last updated | 2026-03-02 | ||
| Replaces | draft-lcurley-moq-transport | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Associated WG milestone |
|
||
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-moq-transport-17
Media Over QUIC S. Nandakumar
Internet-Draft Cisco
Intended status: Standards Track V. Vasiliev
Expires: 3 September 2026 I. Swett, Ed.
Google
A. Frindell, Ed.
Meta
2 March 2026
Media over QUIC Transport
draft-ietf-moq-transport-17
Abstract
This document defines the core behavior for Media over QUIC Transport
(MOQT), a media transport protocol designed to operate over QUIC and
WebTransport, which have similar functionality. MOQT allows a
producer of media to publish data and have it consumed via
subscription by a multiplicity of endpoints. It supports
intermediate content distribution networks and is designed for high
scale and low latency distribution.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at https://moq-
wg.github.io/moq-transport/draft-ietf-moq-transport.html. Status
information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-moq-transport/.
Discussion of this document takes place on the Media Over QUIC
Working Group mailing list (mailto:moq@ietf.org), which is archived
at https://mailarchive.ietf.org/arch/browse/moq/. Subscribe at
https://www.ietf.org/mailman/listinfo/moq/.
Source for this draft and an issue tracker can be found at
https://github.com/moq-wg/moq-transport.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Nandakumar, et al. Expires 3 September 2026 [Page 1]
Internet-Draft moq-transport March 2026
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 3 September 2026.
Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 6
1.1.1. Latency . . . . . . . . . . . . . . . . . . . . . . . 6
1.1.2. Leveraging QUIC . . . . . . . . . . . . . . . . . . . 7
1.1.3. Convergence . . . . . . . . . . . . . . . . . . . . . 7
1.1.4. Relays . . . . . . . . . . . . . . . . . . . . . . . 7
1.2. Terms and Definitions . . . . . . . . . . . . . . . . . . 7
1.3. Stream Management Terms . . . . . . . . . . . . . . . . . 9
1.4. Notational Conventions . . . . . . . . . . . . . . . . . 9
1.4.1. Variable-Length Integers . . . . . . . . . . . . . . 9
1.4.2. Location Structure . . . . . . . . . . . . . . . . . 11
1.4.3. Key-Value-Pair Structure . . . . . . . . . . . . . . 11
1.4.4. Reason Phrase Structure . . . . . . . . . . . . . . . 12
1.5. Representing Namespace and Track Names . . . . . . . . . 13
1.5.1. Parsing Serialized Names . . . . . . . . . . . . . . 13
2. Object Data Model . . . . . . . . . . . . . . . . . . . . . . 14
2.1. Objects . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.2. Subgroups . . . . . . . . . . . . . . . . . . . . . . . . 15
2.3. Groups . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3.1. Group IDs . . . . . . . . . . . . . . . . . . . . . . 17
Nandakumar, et al. Expires 3 September 2026 [Page 2]
Internet-Draft moq-transport March 2026
2.4. Track . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.4.1. Track Naming . . . . . . . . . . . . . . . . . . . . 17
2.4.2. Malformed Tracks . . . . . . . . . . . . . . . . . . 19
2.4.3. Scope . . . . . . . . . . . . . . . . . . . . . . . . 20
2.5. Properties . . . . . . . . . . . . . . . . . . . . . . . 21
3. Sessions . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.1. Session establishment . . . . . . . . . . . . . . . . . . 22
3.1.1. WebTransport . . . . . . . . . . . . . . . . . . . . 22
3.1.2. QUIC . . . . . . . . . . . . . . . . . . . . . . . . 22
3.1.3. Connection URL . . . . . . . . . . . . . . . . . . . 23
3.2. Extension Negotiation . . . . . . . . . . . . . . . . . . 23
3.3. Session initialization . . . . . . . . . . . . . . . . . 24
3.3.1. Request Cancellation and Rejection . . . . . . . . . 24
3.4. Unidirectional Stream Types . . . . . . . . . . . . . . . 24
3.5. Termination . . . . . . . . . . . . . . . . . . . . . . . 25
3.6. Migration . . . . . . . . . . . . . . . . . . . . . . . . 27
3.7. Congestion Control . . . . . . . . . . . . . . . . . . . 27
3.7.1. Bufferbloat . . . . . . . . . . . . . . . . . . . . . 28
3.7.2. Application-Limited . . . . . . . . . . . . . . . . . 28
3.7.3. Consistent Throughput . . . . . . . . . . . . . . . . 28
4. Modularity . . . . . . . . . . . . . . . . . . . . . . . . . 29
5. Publishing and Retrieving Tracks . . . . . . . . . . . . . . 29
5.1. Subscriptions . . . . . . . . . . . . . . . . . . . . . . 29
5.1.1. Subscription State Management . . . . . . . . . . . . 31
5.1.2. Subscription Filters . . . . . . . . . . . . . . . . 32
5.1.3. Joining an Ongoing Track . . . . . . . . . . . . . . 33
5.2. Fetch State Management . . . . . . . . . . . . . . . . . 34
6. Namespace Discovery . . . . . . . . . . . . . . . . . . . . . 34
6.1. Subscribing to Namespaces . . . . . . . . . . . . . . . . 35
6.2. Publishing Namespaces . . . . . . . . . . . . . . . . . . 35
7. Priorities . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 36
7.2. Scheduling Algorithm . . . . . . . . . . . . . . . . . . 37
7.3. Considerations for Setting Priorities . . . . . . . . . . 39
8. Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
8.1. Caching Relays . . . . . . . . . . . . . . . . . . . . . 39
8.2. Forward Handling . . . . . . . . . . . . . . . . . . . . 40
8.3. Multiple Publishers . . . . . . . . . . . . . . . . . . . 40
8.4. Subscriber Interactions . . . . . . . . . . . . . . . . . 41
8.4.1. Graceful Subscriber Relay Switchover . . . . . . . . 42
8.5. Publisher Interactions . . . . . . . . . . . . . . . . . 42
8.5.1. Graceful Publisher Relay Switchover . . . . . . . . . 44
8.6. Relay Track Handling . . . . . . . . . . . . . . . . . . 45
8.7. Relay Object Handling . . . . . . . . . . . . . . . . . . 45
9. Control Messages . . . . . . . . . . . . . . . . . . . . . . 45
9.1. Request ID . . . . . . . . . . . . . . . . . . . . . . . 47
9.2. Required Request ID . . . . . . . . . . . . . . . . . . . 47
9.3. Message Parameters . . . . . . . . . . . . . . . . . . . 47
Nandakumar, et al. Expires 3 September 2026 [Page 3]
Internet-Draft moq-transport March 2026
9.3.1. Parameter Scope . . . . . . . . . . . . . . . . . . . 49
9.3.2. AUTHORIZATION TOKEN Parameter . . . . . . . . . . . . 49
9.3.3. DELIVERY TIMEOUT Parameter . . . . . . . . . . . . . 52
9.3.4. RENDEZVOUS TIMEOUT Parameter . . . . . . . . . . . . 53
9.3.5. SUBSCRIBER PRIORITY Parameter . . . . . . . . . . . . 54
9.3.6. GROUP ORDER Parameter . . . . . . . . . . . . . . . . 54
9.3.7. SUBSCRIPTION FILTER Parameter . . . . . . . . . . . . 54
9.3.8. EXPIRES Parameter . . . . . . . . . . . . . . . . . . 54
9.3.9. LARGEST OBJECT Parameter . . . . . . . . . . . . . . 55
9.3.10. FORWARD Parameter . . . . . . . . . . . . . . . . . . 55
9.3.11. NEW GROUP REQUEST Parameter . . . . . . . . . . . . . 55
9.4. SETUP . . . . . . . . . . . . . . . . . . . . . . . . . . 56
9.4.1. Setup Options . . . . . . . . . . . . . . . . . . . . 57
9.5. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . 59
9.6. REQUEST_OK . . . . . . . . . . . . . . . . . . . . . . . 60
9.7. REQUEST_ERROR . . . . . . . . . . . . . . . . . . . . . . 60
9.8. SUBSCRIBE . . . . . . . . . . . . . . . . . . . . . . . . 62
9.9. SUBSCRIBE_OK . . . . . . . . . . . . . . . . . . . . . . 63
9.10. REQUEST_UPDATE . . . . . . . . . . . . . . . . . . . . . 64
9.10.1. Updating Subscriptions . . . . . . . . . . . . . . . 65
9.11. PUBLISH . . . . . . . . . . . . . . . . . . . . . . . . . 65
9.12. PUBLISH_OK . . . . . . . . . . . . . . . . . . . . . . . 67
9.13. PUBLISH_DONE . . . . . . . . . . . . . . . . . . . . . . 67
9.14. FETCH . . . . . . . . . . . . . . . . . . . . . . . . . . 69
9.14.1. Standalone Fetch . . . . . . . . . . . . . . . . . . 70
9.14.2. Joining Fetches . . . . . . . . . . . . . . . . . . 70
9.14.3. Fetch Handling . . . . . . . . . . . . . . . . . . . 72
9.15. FETCH_OK . . . . . . . . . . . . . . . . . . . . . . . . 74
9.16. TRACK_STATUS . . . . . . . . . . . . . . . . . . . . . . 75
9.17. PUBLISH_NAMESPACE . . . . . . . . . . . . . . . . . . . . 75
9.18. NAMESPACE . . . . . . . . . . . . . . . . . . . . . . . . 76
9.19. NAMESPACE_DONE . . . . . . . . . . . . . . . . . . . . . 77
9.20. SUBSCRIBE_NAMESPACE . . . . . . . . . . . . . . . . . . . 77
9.21. PUBLISH_BLOCKED . . . . . . . . . . . . . . . . . . . . . 79
10. Data Streams and Datagrams . . . . . . . . . . . . . . . . . 80
10.1. Track Alias . . . . . . . . . . . . . . . . . . . . . . 80
10.2. Objects . . . . . . . . . . . . . . . . . . . . . . . . 80
10.2.1. Object Header . . . . . . . . . . . . . . . . . . . 80
10.3. Datagrams . . . . . . . . . . . . . . . . . . . . . . . 82
10.3.1. Object Datagram . . . . . . . . . . . . . . . . . . 83
10.4. Streams . . . . . . . . . . . . . . . . . . . . . . . . 84
10.4.1. Stream Cancellation . . . . . . . . . . . . . . . . 85
10.4.2. Subgroup Header . . . . . . . . . . . . . . . . . . 85
10.4.3. Closing Subgroup Streams . . . . . . . . . . . . . . 87
10.4.4. Fetch Header . . . . . . . . . . . . . . . . . . . . 90
10.5. Examples . . . . . . . . . . . . . . . . . . . . . . . . 93
11. MOQT Properties . . . . . . . . . . . . . . . . . . . . . . . 95
11.1. DELIVERY TIMEOUT . . . . . . . . . . . . . . . . . . . . 95
Nandakumar, et al. Expires 3 September 2026 [Page 4]
Internet-Draft moq-transport March 2026
11.2. MAX CACHE DURATION . . . . . . . . . . . . . . . . . . . 96
11.3. DEFAULT PUBLISHER PRIORITY . . . . . . . . . . . . . . . 96
11.4. DEFAULT PUBLISHER GROUP ORDER . . . . . . . . . . . . . 96
11.5. DYNAMIC GROUPS . . . . . . . . . . . . . . . . . . . . . 97
11.6. Immutable Properties . . . . . . . . . . . . . . . . . . 97
11.7. Prior Group ID Gap . . . . . . . . . . . . . . . . . . . 98
11.8. Prior Object ID Gap . . . . . . . . . . . . . . . . . . 99
12. Security Considerations . . . . . . . . . . . . . . . . . . . 100
12.1. Resource Exhaustion . . . . . . . . . . . . . . . . . . 100
12.2. Timeouts . . . . . . . . . . . . . . . . . . . . . . . . 100
12.2.1. Idle Connection Handling . . . . . . . . . . . . . . 100
12.3. Relay security considerations . . . . . . . . . . . . . 101
12.3.1. State maintenance . . . . . . . . . . . . . . . . . 101
12.3.2. SUBSCRIBE_NAMESPACE with short prefixes . . . . . . 101
12.4. Implementation Identification Fingerprinting . . . . . . 101
13. Grease . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 103
14.1. Authorization Token Alias Type . . . . . . . . . . . . . 103
14.2. MOQT Auth Token Type . . . . . . . . . . . . . . . . . . 103
14.3. Message Parameters . . . . . . . . . . . . . . . . . . . 103
14.4. Properties . . . . . . . . . . . . . . . . . . . . . . . 104
14.5. Error Codes . . . . . . . . . . . . . . . . . . . . . . 105
14.5.1. Session Termination Error Codes . . . . . . . . . . 105
14.5.2. REQUEST_ERROR Codes . . . . . . . . . . . . . . . . 106
14.5.3. PUBLISH_DONE Codes . . . . . . . . . . . . . . . . . 107
14.5.4. Data Stream Reset Error Codes . . . . . . . . . . . 108
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 108
Use of Generative AI . . . . . . . . . . . . . . . . . . . . . . 109
References . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Normative References . . . . . . . . . . . . . . . . . . . . . 109
Informative References . . . . . . . . . . . . . . . . . . . . 110
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 112
A.1. Since draft-ietf-moq-transport-16 . . . . . . . . . . . . 112
A.2. Since draft-ietf-moq-transport-15 . . . . . . . . . . . . 114
A.3. Since draft-ietf-moq-transport-14 . . . . . . . . . . . . 116
A.4. Since draft-ietf-moq-transport-13 . . . . . . . . . . . . 117
A.5. Since draft-ietf-moq-transport-12 . . . . . . . . . . . . 118
A.6. Since draft-ietf-moq-transport-11 . . . . . . . . . . . . 119
A.7. Since draft-ietf-moq-transport-10 . . . . . . . . . . . . 119
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 120
Nandakumar, et al. Expires 3 September 2026 [Page 5]
Internet-Draft moq-transport March 2026
1. Introduction
Media Over QUIC Transport (MOQT) is a protocol that is optimized for
the QUIC protocol [QUIC], either directly or via WebTransport
[WebTransport], for the dissemination of media. MOQT utilizes a
publish/subscribe workflow in which producers of media publish data
in response to subscription requests from a multiplicity of
endpoints. MOQT supports wide range of use-cases with different
resiliency and latency (live, interactive) needs without compromising
the scalability and cost effectiveness associated with content
delivery networks.
MOQT is a generic protocol designed to work in concert with multiple
MoQ Streaming Formats. These MoQ Streaming Formats define how
content is encoded, packaged, and mapped to MOQT objects, along with
policies for discovery and subscription.
* Section 2 describes the data model employed by MOQT.
* Section 3 covers aspects of setting up an MOQT session.
* Section 7 covers mechanisms for prioritizing subscriptions.
* Section 8 covers behavior at the relay entities.
* Section 9 covers how control messages are encoded on the wire.
* Section 10 covers how data messages are encoded on the wire.
1.1. Motivation
The development of MOQT is driven by goals in a number of areas -
specifically latency, the robust feature set of QUIC and relay
support.
1.1.1. Latency
Latency is necessary to correct for variable network throughput.
Ideally live content is consumed at the same bitrate it is produced.
End-to-end latency would be fixed and only subject to encoding and
transmission delays. Unfortunately, networks have variable
throughput, primarily due to congestion. Attempting to deliver
content encoded at a higher bitrate than the network can cause
queuing along the path from producer to consumer. The speed at which
a protocol can detect and respond to congestion determines the
overall latency. TCP-based protocols are simple but are slow to
detect congestion and suffer from head-of-line blocking. Protocols
utilizing UDP directly can avoid queuing, but the application is then
Nandakumar, et al. Expires 3 September 2026 [Page 6]
Internet-Draft moq-transport March 2026
responsible for the complexity of fragmentation, congestion control,
retransmissions, receiver feedback, reassembly, and more. One goal
of MOQT is to achieve the best of both these worlds: leverage the
features of QUIC to create a simple yet flexible low latency protocol
that can rapidly detect and respond to congestion.
1.1.2. Leveraging QUIC
The parallel nature of QUIC streams can provide improvements in the
face of loss. A goal of MOQT is to design a streaming protocol to
leverage the transmission benefits afforded by parallel QUIC streams
as well as exercising options for flexible loss recovery.
1.1.3. Convergence
Some live media architectures today have separate protocols for
ingest and distribution, for example RTMP and HTTP based HLS or DASH.
Switching protocols necessitates intermediary origins which re-
package the media content. While specialization can have its
benefits, there are efficiency gains to be had in not having to re-
package content. A goal of MOQT is to develop a single protocol
which can be used for transmission from contribution to distribution.
A related goal is the ability to support existing encoding and
packaging schemas, both for backwards compatibility and for
interoperability with the established content preparation ecosystem.
1.1.4. Relays
An integral feature of a protocol being successful is its ability to
deliver media at scale. Greatest scale is achieved when third-party
networks, independent of both the publisher and subscriber, can be
leveraged to relay the content. These relays must cache content for
distribution efficiency while simultaneously routing content and
deterministically responding to congestion in a multi-tenant network.
A goal of MOQT is to treat relays as first-class citizens of the
protocol and ensure that objects are structured such that information
necessary for distribution is available to relays while the media
content itself remains opaque and private.
1.2. Terms and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
The following terms are used with the first letter capitalized.
Nandakumar, et al. Expires 3 September 2026 [Page 7]
Internet-Draft moq-transport March 2026
Application: The entity using MOQT to transmit and receive data.
Client: The party initiating a Transport Session.
Server: The party accepting an incoming Transport Session.
Endpoint: A Client or Server.
Peer: The other endpoint than the one being described.
Publisher: An endpoint that handles subscriptions by sending
requested Objects from the requested track.
Subscriber: An endpoint that subscribes to and receives tracks.
Original Publisher: The initial publisher of a given track.
End Subscriber: A subscriber that initiates a subscription and does
not send the data on to other subscribers.
Relay: An entity that is both a Publisher and a Subscriber, is not
the Original Publisher or End Subscriber, and conforms to all
requirements in Section 8.
Upstream: In the direction of the Original Publisher.
Downstream: In the direction of the End Subscriber(s).
Transport Session: A raw QUIC connection or a WebTransport session.
Stream: A bidirectional or unidirectional bytestream provided by the
QUIC transport or WebTransport.
Congestion: Packet loss and queuing caused by degraded or overloaded
networks.
Group: A temporal sequence of objects. A group represents a join
point in a track. See (Section 2.3).
Object: An object is an addressable unit whose payload is a sequence
of bytes. Objects form the base element in the MOQT data model.
See (Section 2.1).
Track: A track is a collection of groups. See (Section 2.4).
Nandakumar, et al. Expires 3 September 2026 [Page 8]
Internet-Draft moq-transport March 2026
1.3. Stream Management Terms
This document uses stream management terms described in [RFC9000],
Section 1.3 including STOP_SENDING, RESET_STREAM and FIN.
1.4. Notational Conventions
This document uses the conventions detailed in ([RFC9000],
Section 1.3) when describing the binary encoding.
1.4.1. Variable-Length Integers
MoQT requires a variable-length integer encoding with the following
properties:
1. The encoded length can be determined from the first encoded byte.
2. The range of 1 byte values is as large as possible.
3. All 64 bit numbers can be encoded.
The variable-length integer encoding uses the number of leading 1
bits of the first byte to indicate the length of the encoding in
bytes. The remaining bits after the first 0 and subsequent bytes, if
any, represent the integer value, encoded in network byte order.
Integers are encoded in 1, 2, 3, 4, 5, 6, 8, or 9 bytes and can
encode up to 64 bit unsigned integers. The following table
summarizes the encoding properties.
Nandakumar, et al. Expires 3 September 2026 [Page 9]
Internet-Draft moq-transport March 2026
+==============+================+========+========================+
| Leading Bits | Length (bytes) | Usable | Range |
| | | Bits | |
+==============+================+========+========================+
| 0 | 1 | 7 | 0-127 |
+--------------+----------------+--------+------------------------+
| 10 | 2 | 14 | 0-16383 |
+--------------+----------------+--------+------------------------+
| 110 | 3 | 21 | 0-2097151 |
+--------------+----------------+--------+------------------------+
| 1110 | 4 | 28 | 0-268435455 |
+--------------+----------------+--------+------------------------+
| 11110 | 5 | 35 | 0-34359738367 |
+--------------+----------------+--------+------------------------+
| 111110 | 6 | 42 | 0-4398046511103 |
+--------------+----------------+--------+------------------------+
| 11111110 | 8 | 56 | 0-72057594037927935 |
+--------------+----------------+--------+------------------------+
| 11111111 | 9 | 64 | 0-18446744073709551615 |
+--------------+----------------+--------+------------------------+
Table 1: Summary of Integer Encodings
The following table contains some example encodings:
+======================+============================+
| Byte Sequence | Decimal Value |
+======================+============================+
| 0x25 | 37 |
+----------------------+----------------------------+
| 0x8025 | 37 |
+----------------------+----------------------------+
| 0xbbbd | 15,293 |
+----------------------+----------------------------+
| 0xdd7f3e7d | 494,878,333 |
+----------------------+----------------------------+
| 0xfaa1a0e403d8 | 2,893,212,287,960 |
+----------------------+----------------------------+
| 0xfefa318fa8e3ca11 | 70,423,237,261,249,041 |
+----------------------+----------------------------+
| 0xffffffffffffffffff | 18,446,744,073,709,551,615 |
+----------------------+----------------------------+
Table 2: Example Integer Encodings
11111100 is an invalid code point. An endpoint that receives this
value MUST close the session with a PROTOCOL_VIOLATION.
Nandakumar, et al. Expires 3 September 2026 [Page 10]
Internet-Draft moq-transport March 2026
To reduce unnecessary use of bandwidth, variable length integers
SHOULD be encoded using the least number of bytes possible to
represent the required value.
x (vi64): Indicates that x holds an integer value using the
variable-length encoding as described above.
1.4.2. Location Structure
Location identifies a particular Object in a Group within a Track.
Location {
Group (vi64),
Object (vi64)
}
Figure 1: Location structure
In this document, a Location can be expressed in the form of
{GroupID, ObjectID}, where GroupID and ObjectID indicate the Group ID
and Object ID of the Location, respectively. The constituent parts
of any Location A can be referred to using A.Group or A.Object.
Location A < Location B if:
A.Group < B.Group || (A.Group == B.Group && A.Object < B.Object)
1.4.3. Key-Value-Pair Structure
Key-Value-Pair is a flexible structure designed to carry key/value
pairs in which the key is a variable length integer and the value is
either a variable length integer or a byte field of arbitrary length.
Key-Value-Pairs encode a Type value as a delta from the previous Type
value, or from 0 if there is no previous Type value. This is
efficient on the wire and makes it easy to ensure there is only one
instance of a type when needed. The previous Type value plus the
Delta Type MUST NOT be greater than 2^64 - 1. If a Delta Type is
received that would be too large, the Session MUST be closed with a
PROTOCOL_VIOLATION.
Key-Value-Pair is used in both the data plane and control plane, but
is optimized for use in the data plane.
Nandakumar, et al. Expires 3 September 2026 [Page 11]
Internet-Draft moq-transport March 2026
Key-Value-Pair {
Delta Type (vi64),
[Length (vi64),]
Value (..)
}
Figure 2: MOQT Key-Value-Pair
* Delta Type: an unsigned integer, encoded as a varint, identifying
the Type as a delta encoded value from the previous Type, if any.
The Type identifies the type of value and also the subsequent
serialization.
* Length: Only present when Type is odd. Specifies the length of
the Value field in bytes. The maximum length of a value is 2^16-1
bytes. If an endpoint receives a length larger than the maximum,
it MUST close the session with a PROTOCOL_VIOLATION.
* Value: A single varint encoded value when Type is even, otherwise
a sequence of Length bytes.
If a receiver understands a Type, and the following Value or Length/
Value does not match the serialization defined by that Type, the
receiver MUST close the session with error code
KEY_VALUE_FORMATTING_ERROR.
1.4.4. Reason Phrase Structure
Reason Phrase provides a way for the sender to encode additional
diagnostic information about the error condition, where appropriate.
Reason Phrase {
Reason Phrase Length (vi64),
Reason Phrase Value (..)
}
* Reason Phrase Length: A variable-length integer specifying the
length of the reason phrase in bytes. The reason phrase length
has a maximum value of 1024 bytes. If an endpoint receives a
length exceeding the maximum, it MUST close the session with a
PROTOCOL_VIOLATION
* Reason Phrase Value: Additional diagnostic information about the
error condition. The reason phrase value is encoded as UTF-8
string and does not carry information, such as language tags, that
would aid comprehension by any entity other than the one that
created the text.
Nandakumar, et al. Expires 3 September 2026 [Page 12]
Internet-Draft moq-transport March 2026
1.5. Representing Namespace and Track Names
There is often a need to render namespace tuples and track names for
purposes such as logging, representing track filenames, or use in
certain authorization verification schemes. The namespace and track
name are binary, so they need to be converted to a safe form.
The following format is RECOMMENDED:
* Each of the namespace tuples are rendered in order with a hyphen
(-) between them followed by the track name with a double hyphen
(--) between the last namespace and track name.
* Bytes in the range a-z, A-Z, 0-9 as well as _ (0x5f) are output as
is, while all other bytes are encoded as a period (.) symbol
followed by exactly two lower case hex digits.
The goal of this format is to have a format that is both filename and
URL safe. It allows many common names to be rendered in an easily
human readable form while still supporting binary values.
1.5.1. Parsing Serialized Names
When parsing a serialized namespace or track name back to its binary
form, implementations MUST apply the following rules to ensure a
canonical encoding:
* The hex digits following a period (.) MUST be lowercase (a-f).
Uppercase hex digits (A-F) are invalid and MUST cause parsing to
fail.
* Bytes that can be represented literally (a-z, A-Z, 0-9, _) MUST
NOT appear in their hex-encoded form. For example, .61 is invalid
because a must be represented as the literal character a. A
parser MUST reject such redundant encodings.
* A period (.) MUST be followed by exactly two hex digits. A
trailing period or a period followed by fewer than two hex digits
is invalid.
These rules ensure that the encoding is bijective: every binary value
has exactly one valid serialized representation, and every valid
serialized string maps to exactly one binary value. This property
simplifies comparison of serialized names without requiring full
deserialization.
Nandakumar, et al. Expires 3 September 2026 [Page 13]
Internet-Draft moq-transport March 2026
Implementations that receive an invalid serialized name SHOULD treat
it as an error. The specific error handling behavior is application-
defined.
Example:
example.2enet-team2-project_x--report
Namespace tuples: (example.net, team2, project_x)
Track name: report
2. Object Data Model
MOQT has a hierarchical data model, comprised of tracks which contain
groups, and groups that contain objects. Inside of a group, the
objects can be organized into subgroups.
To give an example of how an application might use this data model,
consider an application sending high and low resolution video using a
codec with temporal scalability. Each resolution is sent as a
separate track to allow the subscriber to pick the appropriate
resolution given the display environment and available bandwidth.
Each independently coded sequence of pictures in a resolution is sent
as a group as the first picture in the sequence can be used as a
random access point. This allows the client to join at the logical
points where decoding of the media can start without needing
information before the join points. The temporal layers are sent as
separate subgroups to allow the priority mechanism to favor lower
temporal layers when there is not enough bandwidth to send all
temporal layers. Each frame of video is sent as a single object.
2.1. Objects
The basic data element of MOQT is an object. An object is an
addressable unit whose payload is a sequence of bytes. All objects
belong to a group, indicating ordering and potential dependencies
(see Section 2.3). An object is uniquely identified by its track
namespace, track name, group ID, and object ID, and must be an
identical sequence of bytes regardless of how or where it is
retrieved. An Object can become unavailable, but its contents MUST
NOT change over time.
Nandakumar, et al. Expires 3 September 2026 [Page 14]
Internet-Draft moq-transport March 2026
Objects are comprised of two parts: metadata and a payload. The
metadata is never encrypted and is always visible to relays (see
Section 8). The payload portion may be encrypted, in which case it
is only visible to the Original Publisher and End Subscribers. The
Original Publisher is solely responsible for the content of the
object payload. This includes the underlying encoding, compression,
any end-to-end encryption, or authentication. A relay MUST NOT
combine, split, or otherwise modify object payloads.
Objects within a Group are in ascending order by Object ID.
From the perspective of a subscriber or a cache, an Object can be in
three possible states:
1. The Object is known to not exist. This state is permanent. MOQT
has multiple ways to communicate that a certain range of objects
does not exist, including the Object Status field, and the use of
gaps in FETCH responses.
2. The Object is known to exist. From this state, it can transition
to not existing, but not vice versa.
3. The state of the Object is unknown, either because it has not
been yet received, or it has not been produced yet.
Whenever the publisher communicates that certain objects do not
exist, this fact is expressed as a contiguous range of non-existent
objects and by including Properties indicating the group/object gaps;
MOQT implementers should take that into account when selecting
appropriate data structures.
2.2. Subgroups
A subgroup is a sequence of one or more objects from the same group
(Section 2.3) in ascending order by Object ID. Objects in a subgroup
have a dependency and priority relationship consistent with sharing a
stream and are sent on a single stream whenever possible. A Group is
delivered using at least as many streams as there are Subgroups,
typically with a one-to-one mapping between Subgroups and streams.
When an Object's forwarding preference (see Section 10.2.1.2) is
"Datagram", it is not sent in Subgroups, does not belong to a
Subgroup in any way, and the description in the remainder of this
section does not apply.
Nandakumar, et al. Expires 3 September 2026 [Page 15]
Internet-Draft moq-transport March 2026
Streams offer in-order reliable delivery and the ability to cancel
sending and retransmission of data. Furthermore, many QUIC and
WebTransport implementations offer the ability to control the
relative scheduling priority of pending stream data.
Every Object within a Group belongs to exactly one Subgroup or
Datagram.
When Objects are sent in a subscription (see Section 5.1), Objects
from two subgroups MUST NOT be sent on the same stream, and Objects
from the same Subgroup MUST NOT be sent on different streams, unless
one of the streams was reset prematurely, or upstream conditions have
forced objects from a Subgroup to be sent out of Object ID order.
Original publishers assign each Subgroup a Subgroup ID, and do so as
they see fit. The scope of a Subgroup ID is a Group, so Subgroups
from different Groups MAY share a Subgroup ID without implying any
relationship between them. In general, publishers assign objects to
subgroups in order to leverage the features of streams as described
above.
In general, if Object B is dependent on Object A, then delivery of B
can follow A, i.e. A and B can be usefully delivered over a single
stream. If an Object is dependent on all previous Objects in a
Subgroup, it likely fits best in that Subgroup. If an Object is not
dependent on any of the Objects in a Subgroup, it likely belongs in a
different Subgroup.
When assigning Objects to different Subgroups, the Original Publisher
makes a reasonable tradeoff between having an optimal mapping of
Object relationships in a Group and minimizing the number of streams
used.
2.3. Groups
A group is a collection of Objects and is a sub-unit of a Track
(Section 2.4). Groups SHOULD be independently useful, so Objects
within a Group SHOULD NOT depend on Objects in other Groups. A Group
provides a join point for subscriptions, so a subscriber that does
not want to receive the entire Track can opt to receive only Groups
starting from a given Group ID. Groups can contain any number of
Objects.
Nandakumar, et al. Expires 3 September 2026 [Page 16]
Internet-Draft moq-transport March 2026
2.3.1. Group IDs
Within a track, the original publisher SHOULD publish Group IDs which
increase with time (where "time" is defined according to the internal
clock of the media being sent). In some cases, Groups will be
produced in increasing order, but sent to subscribers in a different
order, for example when the subscription's Group Order is Descending.
Due to network reordering and the partial reliability features of
MOQT, Groups can always be received out of order.
As a result, subscribers cannot infer the existence of a Group until
an object in the Group is received. This can create gaps in a cache
that can be filled by doing a Fetch upstream, if necessary.
Applications that cannot produce Group IDs that increase with time
are limited to the subset of MOQT that does not compare group IDs.
Subscribers to these Tracks SHOULD NOT use range filters which span
multiple Groups in FETCH or SUBSCRIBE. SUBSCRIBE and FETCH delivery
use Group Order, so they could have an unexpected delivery order if
Group IDs do not increase with time.
The amount of time elapsed between publishing an Object in Group ID N
and in a Group ID > N, or even which will be published first, is not
defined by this specification and is defined by the applications
using MOQT.
2.4. Track
A track is a sequence of groups (Section 2.3). It is the entity
against which a subscriber issues a subscription request. A
subscriber can request to receive individual tracks starting at a
group boundary, including any new objects pushed by the publisher
while the track is active.
2.4.1. Track Naming
In MOQT, every track is identified by a Full Track Name, consisting
of a Track Namespace and a Track Name.
Track Namespace is an ordered set of between 0 and 32 Track Namespace
Fields, encoded as follows:
Track Namespace {
Number of Track Namespace Fields (vi64),
Track Namespace Field (..) ...
}
Nandakumar, et al. Expires 3 September 2026 [Page 17]
Internet-Draft moq-transport March 2026
* Number of Track Namespace Fields: A variable-length integer
specifying the number of Track Namespace Fields in the Track
Namespace.
Each Track Namespace Field is encoded as follows:
Track Namespace Field {
Track Namespace Field Length (vi64),
Track Namespace Field Value (..)
}
* Track Namespace Field Length: A variable-length integer specifying
the length of the Track Namespace Field in bytes.
* Track Namespace Field Value: A sequence of bytes that forms a
Track Namespace Field.
Each Track Namespace Field Value MUST contain at least one byte. If
an endpoint receives a Track Namespace Field with a Track Namespace
Field Length of 0, it MUST close the session with a
PROTOCOL_VIOLATION.
The structured nature of Track Namespace allows relays and
applications to manipulate prefixes of a namespace. If an endpoint
receives a Track Namespace consisting of greater than 32 Track
Namespace Fields, it MUST close the session with a
PROTOCOL_VIOLATION.
Track Name is a sequence of bytes, possibly empty, that identifies an
individual track within the namespace.
The maximum total length of a Full Track Name is 4,096 bytes. The
length of a Full Track Name is computed as the sum of the Track
Namespace Field Length fields and the Track Name Length field. The
length of a Track Namespace is the sum of the Track Namespace Field
Length fields. If an endpoint receives a Track Namespace or a Full
Track Name exceeding 4,096 bytes, it MUST close the session with a
PROTOCOL_VIOLATION.
In this specification, both the Track Namespace Fields and the Track
Name are not constrained to a specific encoding. They carry a
sequence of bytes and comparison between two Track Namespace Fields
or Track Names is done by exact comparison of the bytes.
Specifications that use MOQT may constrain the information in these
fields, for example by restricting them to UTF-8. Any such
specification needs to specify the canonicalization into the bytes in
the Track Namespace Fields or Track Name such that exact comparison
works.
Nandakumar, et al. Expires 3 September 2026 [Page 18]
Internet-Draft moq-transport March 2026
2.4.2. Malformed Tracks
There are multiple ways a publisher can transmit a Track that does
not conform to MOQT constraints. Such a Track is considered
malformed. Some example conditions that constitute a malformed track
when detected by a receiver include:
1. An Object is received in a FETCH response with the same Group ID
as the previous Object, but whose Object ID is not strictly
larger than the previous object.
2. In a FETCH response, an Object with a particular Subgroup ID is
received, but its Publisher Priority is different from that of
the previous Object with the same Subgroup ID.
3. An Object is received in an Ascending FETCH response whose Group
ID is smaller than the previous Object in the response.
4. An Object is received in a Descending FETCH response whose Group
ID is larger than the previous Object in the response.
5. An Object is received whose Object ID is larger than the final
Object in the Subgroup. The final Object in a Subgroup is the
last Object received on a Subgroup stream before a FIN.
6. A Subgroup is received over multiple transport streams
terminated by FIN with different final Objects.
7. An Object is received in a Group whose Object ID is larger than
the final Object in the Group. The final Object in a Group is
the Object with Status END_OF_GROUP, the last Object before a
FIN in a Subgroup which has the END_OF_GROUP bit set, or the
last Object sent in a FETCH that requested the entire Group.
8. An Object is received on a Track whose Group and Object ID are
larger than the final Object in the Track. The final Object in
a Track is the Object with Status END_OF_TRACK or the last
Object sent in a FETCH whose response indicated End of Track.
9. The same Object is received more than once with different
Payload or other immutable properties.
10. An Object is received with a different Forwarding Preference
than previously observed.
The above list of conditions is not considered exhaustive.
Nandakumar, et al. Expires 3 September 2026 [Page 19]
Internet-Draft moq-transport March 2026
When a subscriber detects a Malformed Track, it MUST cancel any
corresponding subscription or fetches for that Track from that
publisher (see Section 3.3.1), and SHOULD deliver an error to the
application. If a relay detects a Malformed Track, it MUST
immediately terminate downstream subscriptions with PUBLISH_DONE and
reset any fetch streams with Status Code MALFORMED_TRACK. Object(s)
triggering Malformed Track status MUST NOT be cached.
2.4.3. Scope
An MOQT scope is a set of servers (as identified by their connection
URIs) for which a Full Track Name is guaranteed to be unique and
identify a specific track. It is up to the application using MOQT to
define how broad or narrow the scope is. An application that deals
with connections between devices on a local network may limit the
scope to a single connection; by contrast, an application that uses
multiple CDNs to serve media may require the scope to include all of
those CDNs.
Because each Full Track Name is unique within an MOQT scope, they can
be used as a cache key for the track. If, at a given moment in time,
two tracks within the same scope contain different data, they MUST
have different names and/or namespaces. MOQT provides subscribers
with the ability to alter the specific manner in which tracks are
delivered via Parameters, but the actual content of the tracks does
not depend on those parameters; this is in contrast to protocols like
HTTP, where request headers can alter the server response.
A publisher that loses state (e.g. crashes) and intends to resume
publishing on the same Track risks colliding with previously
published Objects and violating the above requirements. A publisher
can handle this in application specific ways, for example:
1. Select a unique Track Name or Track Namespace whenever it resumes
publishing. For example, it can base one of the Namespace Fields
on the current time, or select a sufficiently large random value.
2. Resume publishing under a previous Track Name and Namespace and
set the initial Group ID to a unique value guaranteed to be
larger than all previously used groups. This can be done by
choosing a Group ID based on the current time.
3. Use TRACK_STATUS or similar mechanism to query the previous state
to determine the largest published Group ID.
Nandakumar, et al. Expires 3 September 2026 [Page 20]
Internet-Draft moq-transport March 2026
2.5. Properties
Tracks and Objects can have additional relay-visible fields, known as
Properties, which do not require negotiation, and can be used to
alter MoQT Object distribution.
Properties are defined in Section 11 as well as external
specifications and are registered in an IANA table Section 14. These
specifications define the type and value of the property, along with
any rules concerning processing, modification, caching and
forwarding.
If a Relay does not support a Property, it MUST NOT be modified, MUST
be forwarded, and MUST be cached with the Track or Object. If a
Track or Object arrives with a different set of unknown properties
than previously cached, the most recent set SHOULD replace any cached
values, removing any unknown values not present in the new set.
Relays MUST NOT attempt to merge sets of unknown properties received
in different messages.
If a Relay supports a Property, it MAY be modified, added, removed,
and/or cached, subject to the processing rules specified in the
definition.
Properties are serialized as Key-Value-Pairs (see Figure 2).
Property types are registered in the IANA table 'MOQ Properties'.
See Section 14.
Certain Property type ranges are reserved for application-specific
use and will never be allocated by IANA in future MOQT
specifications:
* 0x38 to 0x3F (1-byte encoding): 8 code points for applications
with tight space constraints
* 0x3800 to 0x3FFF (2-byte encoding): 2048 code points (including
grease Section 13) for applications with moderate space
constraints
Applications MAY use code points in these ranges without registration
for format-specific metadata or other application-defined purposes.
Relays that do not understand the application format MUST forward
these properties unchanged but MUST NOT attempt to interpret their
semantic meaning. Different applications using the same code point
in these ranges may assign different meanings; the interpretation
depends on the track or application context known to the publisher
and subscriber.
Nandakumar, et al. Expires 3 September 2026 [Page 21]
Internet-Draft moq-transport March 2026
3. Sessions
3.1. Session establishment
This document defines a protocol that can be used interchangeably
both over a QUIC connection directly [QUIC], and over WebTransport
[WebTransport]. Both provide streams and datagrams with similar
semantics (see [I-D.ietf-webtrans-overview], Section 4); thus, the
main difference lies in how the servers are identified and how the
connection is established. The QUIC DATAGRAM extension ([RFC9221])
MUST be supported and negotiated in the QUIC connection used for
MOQT, which is already a requirement for WebTransport over HTTP/3.
The RESET_STREAM_AT [I-D.draft-ietf-quic-reliable-stream-reset]
extension to QUIC can be used by MOQT, but the protocol is also
designed to work correctly when the extension is not supported.
There is no definition of the protocol over other transports, such as
TCP, and applications using MoQ might need to fallback to another
protocol when QUIC or WebTransport aren't available.
MOQT uses ALPN in QUIC and "WT-Available-Protocols" in WebTransport
([WebTransport], Section 3.3) to perform version negotiation.
[[RFC editor: please remove the remainder of this section before
publication.]]
The ALPN value [RFC7301] for the final version of this specification
is moqt. ALPNs used to identify IETF drafts are created by appending
the draft number to "moqt-". For example, draft-ietf-moq-
transport-13 would be identified as "moqt-13".
Note: Draft versions prior to -15 all used moq-00 ALPN, followed by
version negotiation in the SETUP messages.
3.1.1. WebTransport
An MOQT server that is accessible via WebTransport can be identified
using an HTTPS URI ([RFC9110], Section 4.2.2). An MOQT session can
be established by sending an extended CONNECT request to the host and
the path indicated by the URI, as described in ([WebTransport],
Section 3).
3.1.2. QUIC
An MOQT server that is accessible via native QUIC can be identified
by a URI with a "moqt" scheme. The "moqt" URI scheme is defined as
follows, using definitions from [RFC3986]:
Nandakumar, et al. Expires 3 September 2026 [Page 22]
Internet-Draft moq-transport March 2026
moqt-URI = "moqt" "://" authority path-abempty [ "?" query ]
The authority portion MUST NOT contain an empty host portion. The
moqt URI scheme supports the /.well-known/ path prefix defined in
[RFC8615].
This protocol does not specify any semantics on the path-abempty and
query portions of the URI. The contents of those are left up to the
application.
The client can establish a connection to an MOQT server identified by
a given URI by setting up a QUIC connection to the host and port
identified by the authority section of the URI. The authority, path-
abempty and query portions of the URI are also transmitted in Setup
Options (see Section 9.4.1). If the port is omitted in the URI, a
default port of 443 is used for setting up the QUIC connection.
3.1.3. Connection URL
Each track MAY have one or more associated connection URLs specifying
network hosts through which a track may be accessed. The syntax of
the Connection URL and the associated connection setup procedures are
specific to the underlying transport protocol usage (see Section 3).
3.2. Extension Negotiation
Endpoints use the exchange of Setup messages to negotiate MOQT
extensions. Extensions can define new Message types, new Parameters,
or new framing for Data Streams and Datagrams.
The client and server MUST include all Setup Options Section 9.4.1
required for the negotiated MOQT version in SETUP.
Each endpoint declares the extensions it supports and provides any
initial values required by those extensions as Setup Options in
SETUP. Once an endpoint has both sent and received SETUP messages,
it determines the set of negotiated extensions.
New versions of MOQT MUST specify which existing extensions can be
used with that version. New extensions MUST specify the existing
versions with which they can be used.
Nandakumar, et al. Expires 3 September 2026 [Page 23]
Internet-Draft moq-transport March 2026
3.3. Session initialization
MOQT uses a pair of unidirectional streams for creating the session
and exchanging control messages. Each peer opens one control stream
beginning with a SETUP message. Using a pair of unidirectional
streams rather than a single bidirectional stream allows either peer
to send data as soon as it is able. Depending on whether 0-RTT is
available on the QUIC connection, either client or server might be
able to send stream data first.
In addition to the control streams, this specification uses
bidirectional streams to carry requests. A request stream begins
with one of these six message types: TRACK_STATUS, SUBSCRIBE,
PUBLISH, FETCH, PUBLISH_NAMESPACE, and SUBSCRIBE_NAMESPACE.
Bidirectional streams MUST NOT begin with any other message type
unless negotiated. If they do, the peer MUST close the Session with
a PROTOCOL_VIOLATION. Objects are sent on unidirectional streams.
Unidirectional streams containing Objects or bidirectional stream(s)
beginning with a request message could arrive prior to the control
streams, in which case the data SHOULD be buffered until both control
streams arrive and setup is complete. If an implementation does not
want to buffer or if the message type is not supported, it MAY reset
such bidirectional streams before the session and control streams are
established.
A control stream MUST NOT be closed at the underlying transport layer
during the session's lifetime. Doing so results in the session being
closed as a PROTOCOL_VIOLATION.
3.3.1. Request Cancellation and Rejection
Once a request stream has been opened, the request MAY be cancelled
by either endpoint. Senders cancel requests if the response is no
longer of interest; Receivers cancel requests if they are unable to
or choose not to respond.
Implementations SHOULD cancel requests by abruptly terminating any
directions of a stream that are still open using RESET_STREAM /
RESET_STREAM_AT or STOP_SENDING.
When an endpoint rejects a request without performing any application
processing, it SHOULD send a REQUEST_ERROR and FIN the stream.
3.4. Unidirectional Stream Types
All unidirectional MOQT streams start with a variable-length integer
indicating the type of the stream.
Nandakumar, et al. Expires 3 September 2026 [Page 24]
Internet-Draft moq-transport March 2026
+===========+==================================+
| ID | Type |
+===========+==================================+
| 0x05 | FETCH_HEADER (Section 10.4.4) |
+-----------+----------------------------------+
| 0x10-0x1D | SUBGROUP_HEADER (Section 10.4.2) |
+-----------+----------------------------------+
| 0x2F00 | SETUP (Section 9.4) |
+-----------+----------------------------------+
Table 3
An endpoint that receives an unknown stream type MUST close the
session.
Control streams (SETUP) are described in Section 3.3. Data streams
(FETCH_HEADER, SUBGROUP_HEADER) are described in Section 10.
3.5. Termination
The Transport Session can be terminated at any point. When native
QUIC is used, the session is closed using the CONNECTION_CLOSE frame
([QUIC], Section 19.19). When WebTransport is used, the session is
closed using the CLOSE_WEBTRANSPORT_SESSION capsule ([WebTransport],
Section 6).
When terminating the Session, the application MAY use any error
message and SHOULD use a relevant code, as defined below:
NO_ERROR (0x0): The session is being terminated without an error.
INTERNAL_ERROR (0x1): An implementation specific error occurred.
UNAUTHORIZED (0x2): The client is not authorized to establish a
session.
PROTOCOL_VIOLATION (0x3): The remote endpoint performed an action
that was disallowed by the specification.
INVALID_REQUEST_ID (0x4): The endpoint received a Request ID with an
incorrect least significant bit for the sender, or a duplicate
Request ID. See Section 9.1.
INVALID_REQUIRED_REQUEST_ID (0x7): The endpoint received a Required
Request ID Delta that results in an invalid Request ID. See
Section 9.2.
DUPLICATE_TRACK_ALIAS (0x5): The endpoint attempted to use a Track
Nandakumar, et al. Expires 3 September 2026 [Page 25]
Internet-Draft moq-transport March 2026
Alias that was already in use.
KEY_VALUE_FORMATTING_ERROR (0x6): The key-value pair has a
formatting error.
INVALID_PATH (0x8): The PATH parameter was used by a server, on a
WebTransport session, or the server does not support the path.
MALFORMED_PATH (0x9): The PATH parameter does not conform to the
rules in Section 9.4.1.2.
GOAWAY_TIMEOUT (0x10): The session was closed because the peer took
too long to close the session in response to a GOAWAY
(Section 9.5) message. See session migration (Section 3.6).
CONTROL_MESSAGE_TIMEOUT (0x11): The session was closed because the
peer took too long to respond to a control message.
DATA_STREAM_TIMEOUT (0x12): The session was closed because the peer
took too long to send data expected on an open Data Stream (see
Section 10). This includes fields of a stream header or an object
header within a data stream. If an endpoint times out waiting for
a new object header on an open subgroup stream, it MAY send a
STOP_SENDING on that stream or terminate the subscription.
AUTH_TOKEN_CACHE_OVERFLOW (0x13): The Session limit Section 9.4.1.3
of the size of all registered Authorization tokens has been
exceeded.
DUPLICATE_AUTH_TOKEN_ALIAS (0x14): Authorization Token attempted to
register an Alias that was in use (see Section 9.3.2).
VERSION_NEGOTIATION_FAILED (0x15): The client didn't offer a version
supported by the server.
MALFORMED_AUTH_TOKEN (0x16): Invalid Auth Token serialization during
registration (see Section 9.3.2).
UNKNOWN_AUTH_TOKEN_ALIAS (0x17): No registered token found for the
provided Alias (see Section 9.3.2).
EXPIRED_AUTH_TOKEN (0x18): Authorization token has expired
(Section 9.3.2).
INVALID_AUTHORITY (0x19): The specified AUTHORITY does not
correspond to this server or cannot be used in this context.
MALFORMED_AUTHORITY (0x1A): The AUTHORITY value is syntactically
Nandakumar, et al. Expires 3 September 2026 [Page 26]
Internet-Draft moq-transport March 2026
invalid.
An endpoint MAY choose to treat a subscription or request specific
error as a session error under certain circumstances, closing the
entire session in response to a condition with a single subscription
or message. Implementations need to consider the impact on other
outstanding subscriptions before making this choice.
3.6. Migration
MOQT requires a long-lived and stateful session. However, a service
provider needs the ability to shutdown/restart a server without
waiting for all sessions to drain naturally, as that can take days
for long-form media. MOQT enables proactively draining sessions via
the GOAWAY message (Section 9.5).
The server sends a GOAWAY message, signaling the client to establish
a new session and migrate any Established subscriptions. The GOAWAY
message optionally contains a new URI for the new session, otherwise
the current URI is reused. The GOAWAY message contains a Timeout
indicating how long, in milliseconds, the sender intends to wait
before closing the session. The sender SHOULD close the session with
GOAWAY_TIMEOUT after the indicated timeout if there are still open
subscriptions or fetches on a connection.
When the server is a subscriber, it SHOULD send a GOAWAY message to
downstream subscribers prior to unsubscribing from upstream
publishers.
After the client receives a GOAWAY, it's RECOMMENDED that the client
waits until there are no more Established subscriptions before
closing the session with NO_ERROR. Ideally this is transparent to
the application using MOQT, which involves establishing a new session
in the background and migrating Established subscriptions and
published namespaces. The client can choose to delay closing the
session if it expects more OBJECTs to be delivered. The sender
closes the session with a GOAWAY_TIMEOUT if the peer doesn't close
the session within the indicated Timeout.
3.7. Congestion Control
MOQT does not specify a congestion controller, but there are
important attributes to consider when selecting a congestion
controller for use with an application built on top of MOQT.
Nandakumar, et al. Expires 3 September 2026 [Page 27]
Internet-Draft moq-transport March 2026
3.7.1. Bufferbloat
Traditional AIMD congestion controllers (ex. CUBIC [RFC9438] and
Reno [RFC6582]) are prone to Bufferbloat. Bufferbloat occurs when
elements along the path build up a substantial queue of packets,
commonly more than doubling the round trip time. These queued
packets cause head-of-line blocking and latency, even when there is
no packet loss.
3.7.2. Application-Limited
The average bitrate for latency sensitive content needs to be less
than the available bandwidth, otherwise data will be queued and/or
dropped. As such, many MOQT applications will typically be limited
by the available data to send, and not the congestion controller.
Many congestion control algorithms only increase the congestion
window or bandwidth estimate if fully utilized. This combination can
lead to underestimating the available network bandwidth. As a
result, applications might need to periodically ensure the congestion
controller is not app-limited for at least a full round trip to
ensure the available bandwidth can be measured.
Some applications might have APIs to allow sending duplicate data or
forward error correction to probe for more bandwidth while also
limiting the impact of probing in case it causes packet loss.
Applications wanting to switch to an alternate representation of a
Track can request that Track at a lower priority to probe.
Applications can subscribe to additional tracks at the lowest (255)
priority to fill the congestion window during probing intervals while
minimizing the impact on higher priority media. Network-assisted
bandwidth estimation mechanisms such as SCONE
[I-D.ietf-scone-protocol] can provide receivers with sustainable
bandwidth hints, which subscribers can use to inform track selection
decisions and potentially avoid unnecessary probing.
3.7.3. Consistent Throughput
Congestion control algorithms are commonly optimized for throughput,
not consistency. For example, BBR's PROBE_RTT state halves the
sending rate for more than a round trip in order to obtain an
accurate minimum RTT. Similarly, Reno halves it's congestion window
upon detecting loss. In both cases, the large reduction in sending
rate might cause issues with latency sensitive applications.
Nandakumar, et al. Expires 3 September 2026 [Page 28]
Internet-Draft moq-transport March 2026
4. Modularity
MOQT defines all messages necessary to implement both simple
publishing or subscribing endpoints as well as highly functional
Relays. Non-Relay endpoints MAY implement only the subset of
functionality required to perform necessary tasks. For example, a
limited media player could operate using only SUBSCRIBE related
messages. Limited endpoints SHOULD respond to any unsupported
messages with the appropriate NOT_SUPPORTED error code, rather than
ignoring them.
Relays MUST implement all MOQT messages defined in this document, as
well as processing rules described in Section 8.
5. Publishing and Retrieving Tracks
5.1. Subscriptions
All subscriptions begin in the Idle state. A subscription can be
initiated and moved to the Pending state by either a publisher or a
subscriber. A publisher initiates a subscription to a track by
sending the PUBLISH message. The subscriber either accepts or
rejects the subscription using PUBLISH_OK or REQUEST_ERROR. A
subscriber initiates a subscription to a track by sending the
SUBSCRIBE message. The publisher either accepts or rejects the
subscription using SUBSCRIBE_OK or REQUEST_ERROR. Once either of
these sequences is successful, the subscription moves to the
Established state and can be updated by the subscriber using
REQUEST_UPDATE. Either endpoint can terminate an Established
subscription, moving it to the Terminated state. The subscriber
terminates a subscription in the Pending (Subscriber) or Established
states by sending STOP_SENDING. The publisher terminates a
subscription in the Pending (Publisher) or Established states by
sending PUBLISH_DONE and closing the stream.
This diagram shows the subscription state machine:
Nandakumar, et al. Expires 3 September 2026 [Page 29]
Internet-Draft moq-transport March 2026
+--------+
| Idle |
+--------+
| |
SUBSCRIBE | | PUBLISH
(subscriber)| | (publisher)
V V
+--------------+ +--------------+
| Pending | | Pending |
+----| (Subscriber) | | (Publisher) |----+
| +--------------+ +--------------+ |
| | | |
REQUEST_ERROR | SUBSCRIBE_OK | | PUBLISH_OK | REQUEST_ERROR
(publisher) | (publisher)| | (subscriber) | (subscriber)
| V V |
| +-------------+ |
| | Established | ------+
| | | | REQUEST_UPDATE
| +-------------+ <-----+
| | | |
+--- STOP_SENDING | | PUBLISH_DONE ----+
| (subscriber)| | (publisher) |
| V V |
| +-------------+ |
+----------->| Terminated | <------------+
+-------------+
A publisher MUST send exactly one SUBSCRIBE_OK or REQUEST_ERROR in
response to a SUBSCRIBE. A subscriber MUST send exactly one
PUBLISH_OK or REQUEST_ERROR in response to a PUBLISH. The peer
SHOULD close the session with a protocol error if it receives more
than one.
All Established subscriptions have a Forward State which is either 0
or 1. The publisher does not send Objects if the Forward State is 0,
and does send them if the Forward State is 1. The initiator of the
subscription sets the initial Forward State in either PUBLISH or
SUBSCRIBE. The subscriber can send PUBLISH_OK or REQUEST_UPDATE to
update the Forward State. Control messages, such as PUBLISH_DONE
(Section 9.13) are sent regardless of the forward state.
A publisher MUST save the Largest Location communicated in
SUBSCRIBE_OK, PUBLISH or REQUEST_OK (in response to a REQUEST_UPDATE)
that changes the Forward State from 0 to 1. This value is called the
Joining Location and can be used in a Joining FETCH (see
Section 9.14.2) while the subscription is in the Established state.
Nandakumar, et al. Expires 3 September 2026 [Page 30]
Internet-Draft moq-transport March 2026
Either endpoint can initiate a subscription to a track without
exchanging any prior messages other than SETUP. Relays MUST NOT send
any PUBLISH messages without knowing the client is interested in and
authorized to receive the content. The communication of intent and
authorization can be accomplished by the client sending
SUBSCRIBE_NAMESPACE, or conveyed in other mechanisms out of band.
An endpoint MAY SUBSCRIBE to a Track it is publishing, though only
Relays are required to handle such a SUBSCRIBE. Such self-
subscriptions are identical to subscriptions initiated by other
endpoints, and all published Objects will be forwarded back to the
endpoint, subject to priority and congestion response rules.
For a given Track, an endpoint can have at most one subscription to a
Track acting as the publisher and at most one acting as a subscriber.
If an endpoint receives a message attempting to establish a second
subscription to a Track with the same role, it MUST fail that request
with a DUPLICATE_SUBSCRIPTION error.
If a publisher receives a SUBSCRIBE request for a Track with an
existing subscription in Pending (publisher) state, it MUST fail that
request with a DUPLICATE_SUBSCRIPTION error. If a subscriber
receives a PUBLISH for a Track with a subscription in the Pending
(Subscriber) state, it MUST ensure the subscription it initiated
transitions to the Terminated state before sending PUBLISH_OK.
A publisher SHOULD begin sending incomplete objects when available to
avoid incurring additional latency.
Publishers MAY start sending Objects on PUBLISH-initiated
subscriptions before receiving a PUBLISH_OK response to reduce
latency. Doing so can consume unnecessary resources in cases where
the Subscriber rejects the subscription with REQUEST_ERROR or sets
Forward State=0 in PUBLISH_OK. It can also result in the Subscriber
dropping Objects if its buffering limits are exceeded (see
Section 10.3 and Section 10.4.2).
5.1.1. Subscription State Management
A subscriber keeps subscription state until it cancels the request
(see Section 3.3.1), or after receipt of a PUBLISH_DONE or
REQUEST_ERROR. Note that PUBLISH_DONE does not usually indicate that
state can immediately be destroyed, see Section 9.13.
The Publisher can destroy subscription state as soon as it has
received STOP_SENDING. It MUST reset any open streams associated
with the SUBSCRIBE.
Nandakumar, et al. Expires 3 September 2026 [Page 31]
Internet-Draft moq-transport March 2026
The Publisher can also immediately delete subscription state after
sending PUBLISH_DONE, but MUST NOT send it until it has closed all
related streams.
A REQUEST_ERROR indicates no objects will be delivered, and both
endpoints can immediately destroy relevant state. Objects MUST NOT
be sent for requests that end with an error.
5.1.2. Subscription Filters
Subscribers can specify a filter on a subscription indicating to the
publisher which Objects to send. Subscriptions without a filter pass
all Objects published or received via upstream subscriptions.
All filters have a Start Location and an optional End Group Delta.
Only objects published or received via a subscription having
Locations greater than or equal to Start Location and strictly less
than or equal to the End Group (when present) pass the filter.
Some filters are defined to be relative to the Largest Object. The
Largest Object is the Object with the largest Location
(Section 1.4.2) in the Track from the perspective of the publisher
processing the message. Largest Object updates when the first byte
of an Object with a Location larger than the previous value is
published or received through a subscription.
A Subscription Filter has the following structure:
Subscription Filter {
Filter Type (vi64),
[Start Location (Location),]
[End Group Delta (vi64),]
}
Filter Type can have one of the following values:
Largest Object (0x2): The filter Start Location is {Largest
Object.Group, Largest Object.Object + 1} and Largest Object is
communicated in SUBSCRIBE_OK. If no content has been delivered yet,
the filter Start Location is {0, 0}. There is no End Group - the
subscription is open ended. Note that due to network reordering or
prioritization, relays can receive Objects with Locations smaller
than Largest Object after the SUBSCRIBE is processed, but these
Objects do not pass the Largest Object filter.
Next Group Start (0x1): The filter Start Location is {Largest
Object.Group + 1, 0} and Largest Object is communicated in
SUBSCRIBE_OK. If no content has been delivered yet, the filter Start
Nandakumar, et al. Expires 3 September 2026 [Page 32]
Internet-Draft moq-transport March 2026
Location is {0, 0}. There is no End Group - the subscription is open
ended. For scenarios where the subscriber intends to start from more
than one group in the future, it can use an AbsoluteStart filter
instead.
AbsoluteStart (0x3): The filter Start Location is specified
explicitly. The specified Start Location MAY be less than the
Largest Object observed at the publisher. There is no End Group -
the subscription is open ended. An AbsoluteStart filter with Start =
{0, 0} is equivalent to an unfiltered subscription.
AbsoluteRange (0x4): The filter Start Location and End Group are
specified explicitly. The specified Start Location MAY be less than
the Largest Object observed at the publisher. If the specified End
Group Delta is zero, the remainder of that Group passes the filter.
Otherwise, the last Group ID to be delivered will be the Group ID in
Start Location plus the End Group Delta.
An endpoint that receives a filter type other than the above MUST
close the session with PROTOCOL_VIOLATION.
5.1.3. Joining an Ongoing Track
The MOQT Object model is designed with the concept that the beginning
of a Group is a join point, so in order for a subscriber to join a
Track, it needs to request an existing Group or wait for a future
Group. Different applications will have different approaches for
when to begin a new Group.
To join a Track at a past Group, the subscriber sends a SUBSCRIBE,
PUBLISH_OK or REQUEST_UPDATE with Forward State 1 followed by a
Joining FETCH (see Section 9.14.2) for the intended start Group,
which can be relative. To join a Track at the next Group, the
subscriber sends a SUBSCRIBE with Filter Type Next Group Start.
5.1.3.1. Dynamically Starting New Groups
While some publishers will deterministically create new Groups, other
applications might want to only begin a new Group when needed. A
subscriber joining a Track might detect that it is more efficient to
request the Original Publisher create a new group than issue a
Joining FETCH. Publishers indicate a Track supports dynamic group
creation using the DYNAMIC_GROUPS parameter (Section 11.5).
One possible subscriber pattern is to SUBSCRIBE to a Track using
Filter Type Largest Object and observe the Largest Location in the
response. If the Object ID is below the application's threshold, the
subscriber sends a FETCH for the beginning of the Group. If the
Nandakumar, et al. Expires 3 September 2026 [Page 33]
Internet-Draft moq-transport March 2026
Object ID is above the threshold and the Track supports dynamic
groups, the subscriber sends a REQUEST_UPDATE message with the
NEW_GROUP_REQUEST parameter equal to the Largest Location's Group,
plus one (see Section 9.3.11).
Another possible subscriber pattern is to send a SUBSCRIBE with
Filter Type Next Group Start and NEW_GROUP_REQUEST equal to 0. The
value of DYNAMIC_GROUPS in SUBSCRIBE_OK will indicate if the
publisher supports dynamic groups. A publisher that does will begin
the next group as soon as practical.
5.2. Fetch State Management
The publisher MUST send exactly one FETCH_OK or REQUEST_ERROR in
response to a FETCH.
A subscriber keeps FETCH state until it cancels the request (see
Section 3.3.1), receives REQUEST_ERROR, or receives a FIN or
RESET_STREAM for the FETCH data stream. If the data stream is
already open, the subscriber wishing to cancel the FETCH MAY send
STOP_SENDING for the data stream as well as the the bidi request
stream. It MUST send STOP_SENDING for the bidi request stream.
The Publisher can destroy fetch state as soon as it has received a
STOP_SENDING. It MUST reset the bidi request stream and
unidirectional data stream associated with the FETCH. It can also
destroy state after closing the FETCH data stream.
It can destroy all FETCH state after closing the data stream with a
FIN.
A REQUEST_ERROR indicates that both endpoints can immediately destroy
state. Since a relay can start delivering FETCH Objects from cache
before determining the result of the request, some Objects could be
received even if the FETCH results in error.
6. Namespace Discovery
Discovery of MOQT servers is always done out-of-band. Namespace
discovery can be done in the context of an established MOQT session.
Given sufficient out of band information, it is valid for a
subscriber to send a SUBSCRIBE or FETCH message to a publisher
(including a relay) without any previous MOQT messages besides SETUP.
However, SUBSCRIBE_NAMESPACE, PUBLISH and PUBLISH_NAMESPACE messages
provide an in-band means of discovery of publishers for a namespace.
The syntax of these messages is described in Section 9.
Nandakumar, et al. Expires 3 September 2026 [Page 34]
Internet-Draft moq-transport March 2026
6.1. Subscribing to Namespaces
If the subscriber is aware of a namespace of interest, it can send
SUBSCRIBE_NAMESPACE to publishers/relays it has established a session
with. The recipient of this message will send any relevant
NAMESPACE, NAMESPACE_DONE or PUBLISH messages for that namespace, or
more specific part of that namespace. This includes echoing back
published Tracks and/or Track Namespaces under the
SUBSCRIBE_NAMESPACE prefix to the endpoint that sent them. If an
endpoint accepts its own PUBLISH, this behaves as self-subscription
described in Section 5.1.
A SUBSCRIBE_NAMESPACE with zero Track Namespace fields indicates the
sender is interested in all tracks and/or namespaces from the
receiver.
The subscriber sends SUBSCRIBE_NAMESPACE on a new bidirectional
stream and the publisher MUST send a single REQUEST_OK or
REQUEST_ERROR as the first message on the bidirectional stream in
response to a SUBSCRIBE_NAMESPACE. The subscriber SHOULD close the
session with a protocol error if it detects receiving more than one.
If a Subscription cannot be created because there is no available
Request ID, the Publisher sends a PUBLISH_BLOCKED message on the
response stream to indicate the Full Track Name of the Subscription
that could not be established. The Publisher MUST NOT send a PUBLISH
for a Track after PUBLISH_BLOCKED has been sent. The subscriber can
instead issue a SUBSCRIBE to establish a subscription to that track.
The receiver of a REQUEST_OK or REQUEST_ERROR ought to forward the
result to the application, so the application can decide which other
publishers to contact, if any.
A SUBSCRIBE_NAMESPACE can be cancelled by closing the stream with
either a FIN or RESET_STREAM. Cancelling does not prohibit original
publishers from sending further PUBLISH_NAMESPACE or PUBLISH
messages, but relays MUST NOT send any further PUBLISH messages to a
client without knowing the client is interested in and authorized to
receive the content.
6.2. Publishing Namespaces
A publisher MAY send PUBLISH_NAMESPACE messages to any subscriber. A
PUBLISH_NAMESPACE indicates to the subscriber that the publisher has
tracks available in that namespace. A subscriber MAY send SUBSCRIBE
or FETCH for tracks in a namespace without having received a
PUBLISH_NAMESPACE for it.
Nandakumar, et al. Expires 3 September 2026 [Page 35]
Internet-Draft moq-transport March 2026
If a publisher is authoritative for a given namespace, or is a relay
that has received an authorized PUBLISH_NAMESPACE for that namespace
from an upstream publisher, it MUST send a PUBLISH_NAMESPACE to any
subscriber that has subscribed via SUBSCRIBE_NAMESPACE for that
namespace, or a prefix of that namespace. A publisher MAY send the
PUBLISH_NAMESPACE to any other subscriber.
An endpoint SHOULD report the reception of a REQUEST_OK or
REQUEST_ERROR to the application to inform the search for additional
subscribers for a namespace, or to abandon the attempt to publish
under this namespace. This might be especially useful in upload or
chat applications. A subscriber MUST send exactly one REQUEST_OK or
REQUEST_ERROR as the first message on the bidi stream in response to
a PUBLISH_NAMESPACE. The publisher SHOULD close the session with a
protocol error if it receives more than one.
A PUBLISH_NAMESPACE is withdrawn by cancelling the request (see
Section 3.3.1), although it is not a protocol error for the
subscriber to send a SUBSCRIBE or FETCH message for a track in a
namespace after the namespace is withdrawn.
A subscriber can cancel the request (see Section 3.3.1) to revoke
acceptance of a PUBLISH_NAMESPACE. If the reason for cancellation is
expiration of authorization credentials, the publisher can send
PUBLISH_NAMESPACE again on a new bidi stream with refreshed
authorization, or close the stream and discard associated state.
While PUBLISH_NAMESPACE indicates to relays how to connect publishers
and subscribers, it is not a full-fledged routing protocol and does
not protect against loops and other phenomena. In particular,
PUBLISH_NAMESPACE SHOULD NOT be used to find paths through richly
connected networks of relays.
A subscriber MAY send a SUBSCRIBE or FETCH for a track to any
publisher. If it has accepted a PUBLISH_NAMESPACE with a namespace
that exactly matches the namespace for that track, it SHOULD only
request it from the senders of those PUBLISH_NAMESPACE messages.
7. Priorities
MoQ priorities allow a subscriber and original publisher to influence
the transmission order of Objects within a session in the presence of
congestion.
7.1. Definitions
MOQT maintains priorities between different schedulable objects. A
schedulable object in MOQT is either:
Nandakumar, et al. Expires 3 September 2026 [Page 36]
Internet-Draft moq-transport March 2026
1. The first or next Object in a Subgroup that is in response to a
subscription.
2. An Object with forwarding preference Datagram.
3. An Object in response to a FETCH where that Object is the next
Object in the response.
An Object is not schedulable if it is known that no part of it can be
written due to underlying transport flow control limits.
A single subgroup or datagram has a single publisher priority.
Within a response to SUBSCRIBE, it can be useful to conceptualize
this process as scheduling subgroups or datagrams instead of
individual objects on them. FETCH responses however can contain
objects with different publisher priorities.
A priority numberis an unsigned integer with a value between 0 and
255. A lower priority number indicates higher priority; the highest
priority is 0.
Subscriber Priority is a priority number associated with an
individual request. It is specified in the SUBSCRIBE or FETCH
message, and can be updated via REQUEST_UPDATE message. The
subscriber priority of an individual schedulable object is the
subscriber priority of the request that caused that object to be
sent. When subscriber priority is changed, a best effort SHOULD be
made to apply the change to all objects that have not been scheduled,
but it is implementation dependent what happens to objects that have
already been scheduled.
Publisher Priority is a priority number associated with an individual
schedulable object. A default can be specified in the parameters of
PUBLISH, or SUBSCRIBE_OK. Publisher priority can also be specified
in a subgroup header or datagram (see Section 10).
Group Order is a property of an individual subscription. It can be
either 'Ascending' (groups with lower group ID are sent first), or
'Descending' (groups with higher group ID are sent first). The
subscriber optionally communicates its group order preference in the
SUBSCRIBE message; the publisher's preference is used if the
subscriber did not express one (by setting Group Order field to value
0x0). The group order of an existing subscription cannot be changed.
7.2. Scheduling Algorithm
When an MOQT publisher has multiple schedulable objects it can choose
between, the objects SHOULD be selected as follows:
Nandakumar, et al. Expires 3 September 2026 [Page 37]
Internet-Draft moq-transport March 2026
1. If two objects have different subscriber priorities associated
with them, the one with *the highest subscriber priority* is
scheduled to be sent first.
2. If two objects have the same subscriber priority, but different
publisher priorities, the one with *the highest publisher
priority* is scheduled to be sent first.
3. If two objects in response to the same request have the same
subscriber and publisher priority, but belong to two different
groups of the same track, *the group order* of the associated
subscription is used to decide the one that is scheduled to be
sent first.
4. If two objects in response to the same request have the same
subscriber and publisher priority and belong to the same group of
the same track, the one with *the lowest Subgroup ID* (for
objects with forwarding preference Subgroup), or *the lowest
Object ID* (for objects with forwarding preference Datagram) is
scheduled to be sent first. If the two objects have different
Forwarding Preferences the order is implementation dependent.
The definition of "scheduled to be sent first" in the algorithm is
implementation dependent and is constrained by the prioritization
interface of the underlying transport. For some implementations, it
could mean that the object is serialized and passed to the underlying
transport first. Other implementations can control the order packets
are initially transmitted.
This algorithm does not provide a well-defined ordering for objects
that belong to different subscriptions or FETCH responses, but have
the same subscriber and publisher priority. The ordering in those
cases is implementation-defined, though the expectation is that all
subscriptions will be able to send some data.
A publisher might not utilize the entire available congestion window,
session flow control, or all available streams for lower priority
Objects if it expects higher priority Objects will be available to
send in the near future or it wants to reserve some bandwidth for
control messages.
Given the critical nature of control messages and their relatively
small size, the control streams SHOULD be prioritized highest,
followed by the bidi request streams and then all subscribed Objects.
Bidi request streams MAY be prioritized within themselves by
Subscriber Priority if specified.
Nandakumar, et al. Expires 3 September 2026 [Page 38]
Internet-Draft moq-transport March 2026
7.3. Considerations for Setting Priorities
For downstream subscriptions, relays SHOULD respect the subscriber
and original publisher's priorities. Relays can receive
subscriptions with conflicting subscriber priorities or Group Order
preferences. Relays SHOULD NOT directly use Subscriber Priority or
Group Order from incoming subscriptions for upstream subscriptions.
Relays' use of these fields for upstream subscriptions can be based
on factors specific to it, such as the popularity of the content or
policy, or relays can specify the same value for all upstream
subscriptions.
MoQ Sessions can span multiple namespaces, and priorities might not
be coordinated across namespaces. The subscriber's priority is
considered first, so there is a mechanism for a subscriber to fix
incompatibilities between different namespaces prioritization
schemes. Additionally, it is anticipated that when multiple
namespaces are present within a session, the namespaces could be
coordinating, possibly part of the same application. In cases when
pooling among namespaces is expected to cause issues, multiple MoQ
sessions, either within a single connection or on multiple
connections can be used.
Implementations that have a default priority SHOULD set it to a value
in the middle of the range (eg: 128) to allow non-default priorities
to be set either higher or lower.
8. Relays
Relays are leveraged to enable distribution scale in the MoQ
architecture. Relays can be used to form an overlay delivery
network, similar in functionality to Content Delivery Networks
(CDNs). Additionally, relays serve as policy enforcement points by
validating subscribe and publish requests at the edge of a network.
Relays are endpoints, which means they terminate Transport Sessions
in order to have visibility of MoQ Object metadata.
8.1. Caching Relays
Relays MAY cache Objects, but are not required to.
Nandakumar, et al. Expires 3 September 2026 [Page 39]
Internet-Draft moq-transport March 2026
A caching relay saves Objects to its cache identified by the Object's
Full Track Name, Group ID and Object ID. If multiple objects are
received with the same Full Track Name, Group ID and Object ID,
Relays MAY ignore subsequently received Objects or MAY use them to
update certain cached fields. Implementations that update the cache
need to protect against cache poisoning. The only Object fields that
can be updated are the following:
1. Object can transition from existing to not existing in cases
where the object is no longer available.
2. Object Properties can be added, removed or updated, subject to
the constraints of the specific property.
An endpoint that receives a duplicate Object with a different
Forwarding Preference, Subgroup ID, Priority or Payload MUST treat
the track as Malformed.
For ranges of objects that do not exist, relays MAY change the
representation of a missing range to a semantically equivalent one.
For instance, a relay may change an End-of-Group="Y" Subgroup Header
to an equivalent object with an End of Group status, or a Prior Group
ID Gap extension could be removed in FETCH, where it's redundant.
Note that due to reordering, an implementation can receive an Object
after receiving an indication that the Object in question does not
exist. The endpoint SHOULD NOT cache or forward the object in this
case.
A cache MUST store all fields of an Object defined in Section 10.2.1,
with the exception of any Object Properties (Section 10.2.1.2) that
specify otherwise.
8.2. Forward Handling
Relays SHOULD set the Forward flag to 1 when a new subscription needs
to be sent upstream, regardless of the value of the Forward field
from the downstream subscription. Subscriptions that are not
forwarded consume resources from the publisher, so a publisher might
deprioritize, reject, or close those subscriptions to ensure other
subscriptions can be delivered.
8.3. Multiple Publishers
A Relay can receive PUBLISH_NAMESPACE for the same Track Namespace or
PUBLISH messages for the same Track from multiple publishers. The
following sections explain how Relays maintain subscriptions to all
available publishers for a given Track.
Nandakumar, et al. Expires 3 September 2026 [Page 40]
Internet-Draft moq-transport March 2026
There is no specified limit to the number of publishers of a Track
Namespace or Track. An implementation can use mechanisms such as
REQUEST_ERROR or unsubscribing (see Section 3.3.1) if it cannot
accept an additional publisher due to implementation constraints.
Implementations can consider the establishment or idle time of the
session or subscription to determine which publisher to reject or
disconnect.
Relays MUST handle Objects for the same Track from multiple
publishers and forward them to matching Established subscriptions.
The Relay SHOULD attempt to deduplicate Objects before forwarding,
subject to implementation constraints.
8.4. Subscriber Interactions
Subscribers request Tracks by sending a SUBSCRIBE (see Section 9.8)
or FETCH (see Section 9.14) control message for each Track of
interest. Relays MUST ensure subscribers are authorized to access
the content associated with the Track. The authorization information
can be part of request itself or part of the encompassing session.
The specifics of how a relay authorizes a user are outside the scope
of this specification.
The relay MUST have an Established upstream subscription before
sending SUBSCRIBE_OK in response to a downstream SUBSCRIBE. If a
relay does not have sufficient information to send a FETCH_OK
immediately in response to a FETCH, it MUST withhold sending FETCH_OK
until it does.
Publishers maintain a list of Established downstream subscriptions
for each Track. Relays use the Track Alias (Section 10.1) of an
incoming Object to identify its Track and find the current
subscribers. Each new Object belonging to the Track is forwarded to
each subscriber, as allowed by the subscription's filter (see
Section 9.8), and delivered according to the priority (see Section 7)
and delivery timeout (see Section 9.3.3).
A relay MUST NOT reorder or drop objects received on a multi-object
stream when forwarding to subscribers, unless it has application
specific information.
Nandakumar, et al. Expires 3 September 2026 [Page 41]
Internet-Draft moq-transport March 2026
Relays MAY aggregate authorized subscriptions for a given Track when
multiple subscribers request the same Track. Subscription
aggregation allows relays to make only a single upstream subscription
for the Track. The published content received from the upstream
subscription request is cached and shared among the pending
subscribers. Because MOQT restricts widening a subscription, relays
that aggregate upstream subscriptions can subscribe using the Largest
Object filter to avoid churn as downstream subscribers with disparate
filters subscribe and unsubscribe from a Track.
A subscriber remains subscribed to a Track at a Relay until it
unsubscribes, the upstream publisher terminates the subscription, or
the subscription expires (see Section 9.9). A subscription with a
filter can reach a state where all possible Objects matching the
filter have been delivered to the subscriber. Since tracking this
can be prohibitively expensive, Relays are not required or expected
to do so.
8.4.1. Graceful Subscriber Relay Switchover
This section describes a behavior that a Subscriber MAY implement to
improve user experience when a relay sends a GOAWAY or the Subscriber
switches between networks, such as WiFi to Cellular, and QUIC
Connection Migration is not possible.
When a subscriber receives the GOAWAY message, it starts the process
of connecting to a new relay and sending the SUBSCRIBE requests for
all Established subscriptions to the new relay. The new relay will
send a response to the subscribes and if they are successful, the
subscriptions to the old relay can be cancelled (see Section 3.3.1).
8.5. Publisher Interactions
There are two ways to publish through a relay:
1. Send a PUBLISH message for a specific Track to the relay. The
relay MAY respond with PUBLISH_OK in Forward State=0 until there
are known subscribers for new Tracks.
2. Send a PUBLISH_NAMESPACE message for a Track Namespace to the
relay. This enables the relay to send SUBSCRIBE or FETCH
messages to publishers for Tracks in this Namespace in response
to requests received from subscribers.
Relays MUST verify that publishers are authorized to publish the set
of Tracks whose Track Namespace matches the namespace in a
PUBLISH_NAMESPACE, or the Full Track Name in PUBLISH. Relays MUST
NOT assume that an authorized publisher of a single Track is
Nandakumar, et al. Expires 3 September 2026 [Page 42]
Internet-Draft moq-transport March 2026
implicitly authorized to publish any other Tracks or Track
Namespaces. If a Publisher would like Subscriptions in a Namespace
routed to it, it MUST send an explicit PUBLISH_NAMESPACE. The
authorization and identification of the publisher depends on the way
the relay is managed and is application specific.
When a publisher wants to stop new subscriptions for a published
namespace, it cancels the request (see Section 3.3.1) to withdraw the
PUBLISH_NAMESPACE. A subscriber indicates it will no longer
subscribe to Tracks in a namespace it previously responded REQUEST_OK
to by cancelling the PUBLISH_NAMESPACE request.
A Relay connects publishers and subscribers by managing sessions
based on the Track Namespace or Full Track Name. When a SUBSCRIBE
message is sent, its Full Track Name is matched exactly against
existing upstream subscriptions.
Namespace Prefix Matching is further used to decide which publishers
receive a SUBSCRIBE and which subscribers receive a PUBLISH. In this
process, the fields in the Track Namespace are matched sequentially,
requiring an exact match for each field. If the published or
subscribed Track Namespace has the same or fewer fields than the
Track Namespace in the message, it qualifies as a match.
For example: A SUBSCRIBE message with namespace=(foo, bar) and name=x
will match sessions that sent PUBLISH_NAMESPACE messages with
namespace=(foo) or namespace=(foo, bar). It will not match a session
with namespace=(foobar).
Relays MUST send SUBSCRIBE messages to all matching publishers. This
includes matching both Established subscriptions on the Full Track
Name and Namespace Prefix Matching against published Namespaces.
Relays MUST forward PUBLISH_NAMESPACE or PUBLISH messages to all
matching subscribers.
When a Relay needs to make an upstream FETCH request, it determines
the available publishers using the same matching rules as SUBSCRIBE.
When more than one publisher is available, the Relay MAY send the
FETCH to any of them.
Nandakumar, et al. Expires 3 September 2026 [Page 43]
Internet-Draft moq-transport March 2026
When a Relay receives an authorized SUBSCRIBE for a Track with one or
more Established upstream subscriptions, it MUST reply with
SUBSCRIBE_OK. If the SUBSCRIBE has Forward State=1 and the upstream
subscriptions are in Forward State=0, the Relay MUST send
REQUEST_UPDATE with Forward=1 to all publishers. If there are no
Established upstream subscriptions for the requested Track, the Relay
MUST send a SUBSCRIBE request to each publisher that has published
the subscription's namespace or prefix thereof. If the SUBSCRIBE has
Forward=1, then the Relay MUST use Forward=1 when subscribing
upstream.
When a relay receives an incoming PUBLISH message, it MUST send a
PUBLISH request to each subscriber that has subscribed (via
SUBSCRIBE_NAMESPACE) to the Track's namespace or prefix thereof.
When a relay receives an authorized PUBLISH_NAMESPACE for a namespace
that matches one or more existing subscriptions to other upstream
sessions, it MUST send a SUBSCRIBE to the publisher that sent the
PUBLISH_NAMESPACE for each matching subscription. When it receives
an authorized PUBLISH message for a Track that has Established
downstream subscriptions, it MUST respond with PUBLISH_OK. If at
least one downstream subscriber for the Track has Forward State=1,
the Relay MUST use Forward State=1 in the reply.
If a Session is closed due to an unknown or invalid control message
or Object, the Relay MUST NOT propagate that message or Object to
another Session, because it would enable a single Session error to
force an unrelated Session, which might be handling other
subscriptions, to be closed.
8.5.1. Graceful Publisher Relay Switchover
This section describes a behavior that a publisher MAY implement to
improve user experience when a relay sends a GOAWAY or the publisher
switches between networks, such as WiFi to Cellular, and QUIC
Connection Migration is not possible.
A new Session is established, to a new URI if specified in a GOAWAY.
The publisher sends PUBLISH_NAMESPACE and/or PUBLISH messages to
begin publishing on the new Session, but it does not immediately stop
publishing Objects on the old Session.
Once the subscriptions have migrated over to the new session, the
publisher can stop publishing Objects on the old session. The relay
will attempt to deduplicate Objects received on both subscriptions.
Ideally, the subscriptions downstream from the relay do not observe
this change, and keep receiving the Objects on the same subscription.
Nandakumar, et al. Expires 3 September 2026 [Page 44]
Internet-Draft moq-transport March 2026
8.6. Relay Track Handling
A relay MUST include all Properties associated with a Track when
sending any PUBLISH, SUBSCRIBE_OK, REQUEST_OK when in response to a
TRACK_STATUS, or FETCH_OK, unless allowed by the property's
specification (see Section 2.5).
8.7. Relay Object Handling
MOQT encodes the delivery information in the Object header
(Section 10.2.1). A relay MUST NOT modify Object fields when
forwarding, except for Object Properties as specified in Section 2.5.
A relay MUST treat the object payload as opaque. A relay MUST NOT
combine, split, or otherwise modify object payloads. A relay SHOULD
prioritize sending Objects based on Section 7.
9. Control Messages
MOQT uses a pair of unidirectional streams to exchange control
messages, as defined in Section 3.3. Every message on a control or
request stream is formatted as follows:
MOQT Control Message {
Message Type (vi64),
Message Length (16),
Message Payload (..),
}
Figure 3: MOQT Control Message
The following Message Types are defined:
+========+============================================+
| ID | Messages |
+========+============================================+
| 0x01 | RESERVED (SETUP for version 00) |
+--------+--------------------------------------------+
| 0x40 | RESERVED (CLIENT_SETUP for versions <= 10) |
+--------+--------------------------------------------+
| 0x41 | RESERVED (SERVER_SETUP for versions <= 10) |
+--------+--------------------------------------------+
| 0x20 | RESERVED (CLIENT_SETUP in versions <= 16) |
+--------+--------------------------------------------+
| 0x21 | RESERVED (SERVER_SETUP in versions <= 16) |
+--------+--------------------------------------------+
| 0x2F00 | SETUP (Section 9.4) |
+--------+--------------------------------------------+
Nandakumar, et al. Expires 3 September 2026 [Page 45]
Internet-Draft moq-transport March 2026
| 0x10 | GOAWAY (Section 9.5) |
+--------+--------------------------------------------+
| 0x7 | REQUEST_OK (Section 9.6) |
+--------+--------------------------------------------+
| 0x5 | REQUEST_ERROR (Section 9.7) |
+--------+--------------------------------------------+
| 0x3 | SUBSCRIBE (Section 9.8) |
+--------+--------------------------------------------+
| 0x4 | SUBSCRIBE_OK (Section 9.9) |
+--------+--------------------------------------------+
| 0x2 | REQUEST_UPDATE (Section 9.10) |
+--------+--------------------------------------------+
| 0x1D | PUBLISH (Section 9.11) |
+--------+--------------------------------------------+
| 0x1E | PUBLISH_OK (Section 9.12) |
+--------+--------------------------------------------+
| 0xB | PUBLISH_DONE (Section 9.13) |
+--------+--------------------------------------------+
| 0x16 | FETCH (Section 9.14) |
+--------+--------------------------------------------+
| 0x18 | FETCH_OK (Section 9.15) |
+--------+--------------------------------------------+
| 0xD | TRACK_STATUS (Section 9.16) |
+--------+--------------------------------------------+
| 0x6 | PUBLISH_NAMESPACE (Section 9.17) |
+--------+--------------------------------------------+
| 0x8 | NAMESPACE (Section 9.18) |
+--------+--------------------------------------------+
| 0xE | NAMESPACE_DONE (Section 9.19) |
+--------+--------------------------------------------+
| 0x11 | SUBSCRIBE_NAMESPACE (Section 9.20) |
+--------+--------------------------------------------+
| 0xF | PUBLISH_BLOCKED (Section 9.21) |
+--------+--------------------------------------------+
Table 4
An endpoint that receives an unknown message type MUST close the
session. Control messages have a length to make parsing easier, but
no control messages are intended to be ignored. The length is set to
the number of bytes in Message Payload, which is defined by each
message type. If the length does not match the length of the Message
Payload, the receiver MUST close the session with a
PROTOCOL_VIOLATION.
Nandakumar, et al. Expires 3 September 2026 [Page 46]
Internet-Draft moq-transport March 2026
9.1. Request ID
Request ID is included in request messages and is used to identify
requests across messages. For example, Joining Fetch references the
Request ID of a SUBSCRIBE.
The client generates even numbered Request IDs, starting at 0, and
the server generates odd numbered Request IDs, starting at 1. Each
endpoint increments its Request ID by 2 for each new request.
Each SUBSCRIBE, PUBLISH, FETCH, SUBSCRIBE_NAMESPACE,
PUBLISH_NAMESPACE, REQUEST_UPDATE, and TRACK_STATUS message consumes
a Request ID. Only request messages include a Request ID; response
messages do not, since they are sent on the same bidirectional stream
as the request.
If an endpoint receives a Request ID where the least significant bit
is incorrect for the sender, or a duplicate Request ID, it MUST close
the session with INVALID_REQUEST_ID.
9.2. Required Request ID
Every request message includes a Required Request ID Delta field that
specifies a dependency on a prior request. The Required Request ID
is computed as:
Required Request ID = Request ID - (2 × Required Request ID
Delta)
A Required Request ID Delta of 0 indicates no dependency. When a
dependency exists, the receiver MUST deliver the referenced request
to the application before delivering the dependent request. If the
required request does not arrive, the receiver will time out the
dependent request.
The delta is scaled by two because request IDs from each endpoint use
alternating parity (odd or even), so valid dependencies always differ
by a multiple of two. An endpoint MUST close the session with
INVALID_REQUIRED_REQUEST_ID if it receives a delta where 2 × Required
Request ID Delta exceeds the Request ID.
9.3. Message Parameters
Some control messages include a field that encodes optional Message
Parameters. Message Parameters are serialized as follows:
Nandakumar, et al. Expires 3 September 2026 [Page 47]
Internet-Draft moq-transport March 2026
Message Parameter {
Type Delta (vi64),
Value (..)
}
Figure 4: Message Parameter
Type Delta: The difference between this Parameter Type and the
previous Parameter Type in the message, or the Parameter Type itself
for the first parameter. Parameters MUST be serialized in ascending
order by Type.
* Value: The encoding is specified by each parameter definition.
The encodings defined in this draft are:
- uint8: A single-byte unsigned integer (0-255)
- varint: A variable-length integer
- Location: Two consecutive varints (Group, Object)
- Length-prefixed: A varint length followed by that many bytes
Message Parameters are intended for the peer only and are not
forwarded by Relays, though relays can consider received parameter
values when making a request.
All Message Parameters MUST be defined in the negotiated version of
MOQT or negotiated via Setup Options. An endpoint that receives an
unknown Message Parameter MUST close the session with
PROTOCOL_VIOLATION. Because the receiver has to understand every
Message Parameter, there is no need for a mechanism to skip unknown
parameters.
The Message Parameter types defined in this version of MOQT are
listed below.
Senders MUST NOT repeat the same Parameter Type in a message unless
the parameter definition explicitly allows multiple instances of that
type to be sent in a single message. Receivers SHOULD check that
there are no unexpected duplicate parameters and close the session
with PROTOCOL_VIOLATION if found.
The number of Message Parameters is not specifically limited, but the
total length of a control message is limited to 2^16-1 bytes.
Nandakumar, et al. Expires 3 September 2026 [Page 48]
Internet-Draft moq-transport March 2026
Message Parameters in SUBSCRIBE, PUBLISH_OK and FETCH MUST NOT cause
the publisher to alter the payload of the objects it sends, as that
would violate the track uniqueness guarantee described in
Section 2.4.3.
Message Parameters in SUBSCRIBE, PUBLISH_OK and FETCH MUST NOT cause
the publisher to alter the payload of the objects it sends, as that
would violate the track uniqueness guarantee described in
Section 2.4.3.
9.3.1. Parameter Scope
Message Parameters are always intended for the peer endpoint only and
are not forwarded by Relays, though relays can consider received
parameter values when making a request. Track information not
specific to the Message or Session is encoded in Track Properties.
See Section 2.5.
Each Message Parameter definition indicates the message types in
which it can appear. If it appears in some other type of message,
the receiving endpoint MUST close the connection with a
PROTOCOL_VIOLATION. Note that since Setup Options use a separate
namespace, it is impossible for Message Parameters to appear in Setup
messages.
9.3.2. AUTHORIZATION TOKEN Parameter
The AUTHORIZATION TOKEN parameter (Parameter Type 0x03) uses Length-
prefixed encoding. It MAY appear in a PUBLISH, SUBSCRIBE,
REQUEST_UPDATE, SUBSCRIBE_NAMESPACE, PUBLISH_NAMESPACE, TRACK_STATUS
or FETCH message. This parameter conveys information to authorize
the sender to perform the operation carrying the parameter.
The parameter value is a Token structure containing an optional
Session-specific Alias. The Alias allows the sender to reference a
previously transmitted Token Type and Token Value in future messages.
The Token structure is serialized as follows:
Token {
Alias Type (vi64),
[Token Alias (vi64),]
[Token Type (vi64),]
[Token Value (..)]
}
Figure 5: Token structure
Nandakumar, et al. Expires 3 September 2026 [Page 49]
Internet-Draft moq-transport March 2026
* Alias Type - an integer defining both the serialization and the
processing behavior of the receiver. This Alias type has the
following code points:
DELETE (0x0): There is an Alias but no Type or Value. This Alias
and the Token Value it was previously associated with| MUST be
retired. Retiring removes them from the pool of actively
registered tokens.
REGISTER (0x1): There is an Alias, a Type and a Value. This Alias
MUST be associated with the Token Value for the duration of the
Session or it is deleted. This action is termed "registering" the
Token.
USE_ALIAS (0x2): There is an Alias but no Type or Value. Use the
Token Type and Value previously registered with this Alias.
USE_VALUE (0x3): There is no Alias and there is a Type and Value.
Use the Token Value as provided. The Token Value may be discarded
after processing.
If a server receives Alias Type DELETE (0x0) or USE_ALIAS (0x2) in a
SETUP message, it MUST close the session with a PROTOCOL_VIOLATION.
* Token Alias - a Session-specific integer identifier that
references a Token Value. There are separate Alias spaces for the
client and server (e.g.: they can each register Alias=1). Once a
Token Alias has been registered, it cannot be re-registered by the
same endpoint in the Session without first being deleted. Use of
the Token Alias is optional.
* Token Type - a numeric identifier for the type of Token payload
being transmitted. This type is defined by the IANA table "MOQT
Auth Token Type" (see Section 14). Type 0 is reserved to indicate
that the type is not defined in the table and is negotiated out-
of-band between client and receiver.
* Token Value - the payload of the Token. The contents and
serialization of this payload are defined by the Token Type.
If the Token structure cannot be decoded, the receiver MUST close the
Session with KEY_VALUE_FORMATTING_ERROR. The receiver of a message
attempting to register an Alias which is already registered MUST
close the Session with DUPLICATE_AUTH_TOKEN_ALIAS. The receiver of a
message referencing an Alias that is not currently registered MUST
reject the message with UNKNOWN_AUTH_TOKEN_ALIAS.
Nandakumar, et al. Expires 3 September 2026 [Page 50]
Internet-Draft moq-transport March 2026
The receiver of a message containing a well-formed Token structure
but otherwise invalid AUTHORIZATION TOKEN parameter MUST reject that
message with an MALFORMED_AUTH_TOKEN error.
The receiver of a message carrying an AUTHORIZATION TOKEN with Alias
Type REGISTER that does not result in a Session error MUST register
the Token Alias, in the token cache, even if the message fails for
other reasons, including Unauthorized. This allows senders to
pipeline messages that refer to previously registered tokens without
potentially terminating the entire Session. A receiver MAY store an
error code (eg: UNAUTHORIZED or MALFORMED_AUTH_TOKEN) in place of the
Token Type and Token Alias if any future message referencing the
Token Alias will result in that error. However, it is important to
not store an error code for a token that might be valid in the future
or due to some other property becoming fulfilled which currently
isn't. The size of a registered cache entry includes the length of
the Token Value, regardless of whether it is stored.
If a receiver detects that an authorization token has expired, it
MUST retain the registered Alias until it is deleted by the sender,
though it MAY discard other state associated with the token that is
no longer needed. Expiration does not affect the size occupied by a
token in the token cache. Any message that references the token with
Alias Type USE_ALIAS fails with EXPIRED_AUTH_TOKEN.
Using an Alias to refer to a previously registered Token Type and
Value is for efficiency only and has the same effect as if the Token
Type and Value was included directly. Retiring an Alias that was
previously used to authorize a message has no retroactive effect on
the original authorization, nor does it prevent that same Token Type
and Value from being re-registered.
Senders of tokens SHOULD only register tokens which they intend to
re-use during the Session and SHOULD retire previously registered
tokens once their utility has passed.
By registering a Token, the sender is requiring the receiver to store
the Token Alias and Token Value until they are deleted, or the
Session ends. The receiver can protect its resources by sending a
Setup Option defining the MAX_AUTH_TOKEN_CACHE_SIZE limit (see
Section 9.4.1.3) it is willing to accept. If a registration is
attempted which would cause this limit to be exceeded, the receiver
MUST terminate the Session with a AUTH_TOKEN_CACHE_OVERFLOW error.
The AUTHORIZATION TOKEN parameter MAY be repeated within a message as
long as the combination of Token Type and Token Value are unique
after resolving any aliases.
Nandakumar, et al. Expires 3 September 2026 [Page 51]
Internet-Draft moq-transport March 2026
Messages carrying the AUTHORIZATION TOKEN parameter can appear on
different control streams. Because stream processing order can be
different than send order, the receiver and sender can have
inconsistent views of the token cache state.
Senders MUST NOT send USE_ALIAS on one control stream for an alias
registered on a different stream until the sender has received a
response to the message containing the REGISTER. Senders MAY use
USE_ALIAS on the same control stream as the REGISTER without waiting
for a response.
Senders MUST NOT send DELETE for an alias while any message using
USE_ALIAS with that alias has not received a response.
9.3.3. DELIVERY TIMEOUT Parameter
The DELIVERY TIMEOUT parameter (Parameter Type 0x02) is a varint. It
MAY appear in a PUBLISH_OK, SUBSCRIBE, or REQUEST_UPDATE message.
It is the duration in milliseconds the relay SHOULD continue to
attempt forwarding Objects after they have been received. The start
time for the timeout is based on when the Object header is received,
and does not depend upon the forwarding preference. Objects with
forwarding preference 'Datagram' are not retransmitted when lost, so
the Delivery Timeout only limits the amount of time they can be
queued before being sent. There is no explicit signal that an Object
was not sent because the delivery timeout was exceeded.
A DELIVERY_TIMEOUT value of 0 indicates no timeout; Objects do not
expire due to delivery timeout.
If both the subscriber specifies this parameter and the Track has a
DELIVERY_TIMEOUT extension, the endpoints use the min of the two non-
zero values for the subscription. If either value is 0, the non-zero
value is used. If both are 0, there is no delivery timeout.
Publishers can, at their discretion, discontinue forwarding Objects
earlier than the negotiated DELIVERY TIMEOUT, subject to stream
closure and ordering constraints described in Section 10.4.3.
However, if neither the subscriber nor publisher specifies DELIVERY
TIMEOUT, all Objects in the track matching the subscription filter
are delivered as indicated by their Group Order and Priority. If a
subscriber fails to consume Objects at a sufficient rate, causing the
publisher to exceed its resource limits, the publisher MAY terminate
the subscription using PUBLISH_DONE with error TOO_FAR_BEHIND.
Nandakumar, et al. Expires 3 September 2026 [Page 52]
Internet-Draft moq-transport March 2026
If an object in a subgroup exceeds the delivery timeout, the
publisher MUST reset the underlying transport stream (see
Section 10.4.3) and SHOULD NOT attempt to open a new stream to
deliver additional Objects in that Subgroup.
This parameter is intended to be specific to a subscription, so it
SHOULD NOT be forwarded upstream by a relay that intends to serve
multiple subscriptions for the same track.
Publishers SHOULD consider whether the entire Object can likely be
successfully delivered within the timeout period before sending any
data for that Object, taking into account priorities, congestion
control, and any other relevant information.
9.3.4. RENDEZVOUS TIMEOUT Parameter
The RENDEZVOUS_TIMEOUT parameter (Parameter Type 0x04) MAY appear in
a SUBSCRIBE message.
It is the duration in milliseconds the subscriber is willing to wait
for a publisher to become available. This applies when a relay
receives a SUBSCRIBE for a Track that has no current publisher.
If the RENDEZVOUS_TIMEOUT is present, the relay SHOULD hold the
subscription and wait for a publisher to appear, up to the specified
duration. The relay does not send SUBSCRIBE_OK until a publisher
becomes available. If a publisher becomes available within this
time, the relay proceeds with the subscription normally. If the
timeout expires without a publisher, the relay SHOULD respond with
REQUEST_ERROR with error code TIMEOUT.
The relay MAY use a shorter timeout than requested by the subscriber.
For example, a relay might limit the maximum rendezvous timeout to
protect its resources.
A value of 0 indicates the subscriber does not want to wait and
expects an immediate response. The relay MUST immediately return
REQUEST_ERROR with error code DOES_NOT_EXIST if no publisher is
available
If RENDEZVOUS_TIMEOUT is absent, the default is 0.
Nandakumar, et al. Expires 3 September 2026 [Page 53]
Internet-Draft moq-transport March 2026
9.3.5. SUBSCRIBER PRIORITY Parameter
The SUBSCRIBER_PRIORITY parameter (Parameter Type 0x20) is a uint8.
It MAY appear in a SUBSCRIBE, FETCH, REQUEST_UPDATE (for a
subscription or FETCH), or PUBLISH_OK message. It is an integer
expressing the priority of a subscription relative to other
subscriptions and fetch responses in the same session. Lower numbers
get higher priority. See Section 7.
If omitted from SUBSCRIBE, PUBLISH_OK or FETCH, the publisher uses
the value 128.
9.3.6. GROUP ORDER Parameter
The GROUP_ORDER parameter (Parameter Type 0x22) is a uint8. It MAY
appear in a SUBSCRIBE, PUBLISH_OK, or FETCH.
Its value indicates how to prioritize Objects from different groups
within the same subscription (see Section 7), or how to order Groups
in a Fetch response (see Section 9.14.3). The allowed values are
Ascending (0x1) or Descending (0x2). If an endpoint receives a value
outside this range, it MUST close the session with
PROTOCOL_VIOLATION.
If omitted from SUBSCRIBE, the publisher's preference from the Track
is used. If omitted from FETCH, the receiver uses Ascending (0x1).
9.3.7. SUBSCRIPTION FILTER Parameter
The SUBSCRIPTION_FILTER parameter (Parameter Type 0x21) uses length-
prefixed encoding. It MAY appear in a SUBSCRIBE, PUBLISH_OK or
REQUEST_UPDATE (for a subscription) message. It is a Subscription
Filter (see Section 5.1.2).
If omitted from SUBSCRIBE or PUBLISH_OK, the subscription is
unfiltered. If omitted from REQUEST_UPDATE, the value is unchanged.
9.3.8. EXPIRES Parameter
The EXPIRES parameter (Parameter Type 0x8) is a varint. It MAY
appear in SUBSCRIBE_OK, PUBLISH, PUBLISH_OK, or REQUEST_OK. It
encodes the time in milliseconds after which the sender of the
parameter will terminate the subscription. The sender will terminate
the subscription using PUBLISH_DONE or by cancelling the request (see
Section 3.3.1). This value is advisory and the sender can terminate
the subscription prior to or after the expiry time.
Nandakumar, et al. Expires 3 September 2026 [Page 54]
Internet-Draft moq-transport March 2026
The receiver of the parameter can attempt to extend the subscription
by sending a REQUEST_UPDATE with 0 or more updated parameters. If
the receiver has one or more updated AUTHORIZATION_TOKENs, it SHOULD
include those in the REQUEST_UPDATE. If the extension is granted,
the sender includes a new EXPIRES value in REQUEST_OK. Relays that
send this parameter and applications that receive it MAY introduce
jitter to prevent many endpoints from updating simultaneously.
If the EXPIRES parameter is 0 or is not present in a message, the
subscription does not expire or expires at an unknown time.
9.3.9. LARGEST OBJECT Parameter
The LARGEST_OBJECT parameter (Parameter Type 0x9) is a Location. It
MAY appear in SUBSCRIBE_OK, PUBLISH or in REQUEST_OK (in response to
REQUEST_UPDATE or TRACK_STATUS). It contains the largest Location
(see Section 1.4.2) in the Track observed by the sending endpoint
(see Section 5.1.2). If Objects have been published on this Track
the Publisher MUST include this parameter.
If omitted from a message, the sending endpoint has not published or
received any Objects in the Track.
9.3.10. FORWARD Parameter
The FORWARD parameter (Parameter Type 0x10) is a uint8. It MAY
appear in SUBSCRIBE, REQUEST_UPDATE (for a subscription), PUBLISH,
PUBLISH_OK and SUBSCRIBE_NAMESPACE. It specifies the Forwarding
State on affected subscriptions (see Section 5.1). The allowed
values are 0 (don't forward) or 1 (forward). If an endpoint receives
a value outside this range, it MUST close the session with
PROTOCOL_VIOLATION.
If the parameter is omitted from REQUEST_UPDATE, the value for the
subscription remains unchanged. If the parameter is omitted from any
other message, the default value is 1.
9.3.11. NEW GROUP REQUEST Parameter
The NEW_GROUP_REQUEST parameter (Parameter Type 0x32) is a varint.
It MAY appear in PUBLISH_OK, SUBSCRIBE or REQUEST_UPDATE for a
subscription. It represents the largest Group ID in the Track known
by the subscriber, plus 1. A value of 0 indicates that the
subscriber has no Group information for the Track. A subscriber MUST
NOT send this parameter in PUBLISH_OK or REQUEST_UPDATE if the Track
did not include the DYNAMIC_GROUPS Property with value 1. A
subscriber MAY include this parameter in SUBSCRIBE without
foreknowledge of support. If the original publisher does not support
Nandakumar, et al. Expires 3 September 2026 [Page 55]
Internet-Draft moq-transport March 2026
dynamic Groups, it ignores the parameter in that case.
When an Original Publisher that supports dynamic Groups receives a
NEW_GROUP_REQUEST with a value of 0 or a value larger than the
current Group, it SHOULD end the current Group and begin a new Group
as soon as practical. The Original Publisher MAY delay the
NEW_GROUP_REQUEST subject to implementation specific concerns, for
example, achieving a minimum duration for each Group. The Original
Publisher chooses the next Group ID; there are no requirements that
it be equal to the NEW_GROUP_REQUEST parameter value.
Relay Handling:
A relay that receives a NEW_GROUP_REQUEST for a Track without an
Established subscription MUST include the NEW_GROUP_REQUEST when
subscribing upstream.
A relay that receives a NEW_GROUP_REQUEST for an Established
subscription with a value of 0 or a value larger than the Largest
Group MUST send a REQUEST_UPDATE including the NEW_GROUP_REQUEST to
the publisher unless:
1. The Track does not support dynamic Groups
2. There is already an outstanding NEW_GROUP_REQUEST from this Relay
with a greater or equal value
If a relay receives a NEW_GROUP_REQUEST with a non-zero value less
than or equal to the Largest Group, it does not send a
NEW_GROUP_REQUEST upstream.
After sending a NEW_GROUP_REQUEST upstream, the request is considered
outstanding until the Largest Group increases.
9.4. SETUP
The SETUP message is the first message each endpoint sends on its
control stream (see Section 3.3); it allows the endpoints to agree on
the initial configuration before any other control messages are
exchanged. An endpoint that is not offering extensions which modify
control message semantics MAY pipeline other control messages after
SETUP without waiting for the peer's SETUP.
The messages contain a sequence of key-value pairs called Setup
Options; the semantics and format of which can vary based on whether
the client or server is sending. To ensure future extensibility of
MOQT, endpoints MUST ignore unknown Setup Options.
Nandakumar, et al. Expires 3 September 2026 [Page 56]
Internet-Draft moq-transport March 2026
The wire format of the Setup message is as follows:
SETUP Message {
Type (vi64) = 0x2F00,
Length (16),
Setup Options (..) ...,
}
Figure 6: MOQT SETUP Message
Setup Options are serialized as Key-Value-Pairs Figure 2. Setup
Options use a namespace that is constant across all MOQT versions,
separate from Message Parameters. Receivers MUST ignore unrecognized
Setup Options. Senders MUST NOT repeat the same Option Type in a
message unless the option definition explicitly allows multiple
instances. Receivers MUST allow duplicates of unknown Setup Options.
The available Setup Options are detailed in the next sections.
9.4.1. Setup Options
9.4.1.1. AUTHORITY
The AUTHORITY option (Option Type 0x05) allows the client to specify
the authority component of the MoQ URI when using native QUIC
([QUIC]). It MUST NOT be used by the server, or when WebTransport is
used. When an AUTHORITY option is received from a server, or when an
AUTHORITY option is received while WebTransport is used, or when an
AUTHORITY option is received by a server but the server does not
support the specified authority, the session MUST be closed with
INVALID_AUTHORITY.
The AUTHORITY option follows the URI formatting rules [RFC3986].
When connecting to a server using a URI with the "moqt" scheme, the
client MUST set the AUTHORITY option to the authority portion of the
URI. If an AUTHORITY option does not conform to these rules, the
session MUST be closed with MALFORMED_AUTHORITY.
9.4.1.2. PATH
The PATH option (Option Type 0x01) allows the client to specify the
path of the MoQ URI when using native QUIC ([QUIC]). It MUST NOT be
used by the server, or when WebTransport is used. When a PATH option
is received from a server, or when a PATH option is received while
WebTransport is used, or when a PATH option is received by a server
but the server does not support the specified path, the session MUST
be closed with INVALID_PATH.
Nandakumar, et al. Expires 3 September 2026 [Page 57]
Internet-Draft moq-transport March 2026
The PATH option follows the URI formatting rules [RFC3986]. When
connecting to a server using a URI with the "moqt" scheme, the client
MUST set the PATH option to the path-abempty portion of the URI; if
query is present, the client MUST concatenate ?, followed by the
query portion of the URI to the option. If a PATH does not conform
to these rules, the session MUST be closed with MALFORMED_PATH.
9.4.1.3. MAX_AUTH_TOKEN_CACHE_SIZE
The MAX_AUTH_TOKEN_CACHE_SIZE option (Option Type 0x04) communicates
the maximum size in bytes of all actively registered Authorization
tokens that the endpoint is willing to store per Session. This
option is optional. The default value is 0 which prohibits the use
of token Aliases.
The token size is calculated as 16 bytes + the size of the Token
Value field (see Figure 5). The total size as restricted by the
MAX_AUTH_TOKEN_CACHE_SIZE option is calculated as the sum of the
token sizes for all registered tokens (Alias Type value of 0x01)
minus the sum of the token sizes for all deregistered tokens (Alias
Type value of 0x00), since Session initiation.
9.4.1.4. AUTHORIZATION TOKEN
The AUTHORIZATION TOKEN Setup Option (Option Type 0x03) is
functionally equivalent to the AUTHORIZATION TOKEN message parameter,
see Section 9.3.2. The endpoint can specify one or more tokens in
SETUP that the peer can use to authorize MOQT session establishment.
If an endpoint receives an AUTHORIZATION TOKEN option in SETUP with
Alias Type REGISTER that exceeds its MAX_AUTH_TOKEN_CACHE_SIZE, it
MUST NOT fail the session with AUTH_TOKEN_CACHE_OVERFLOW. Instead,
it MUST treat the option as Alias Type USE_VALUE. Since each
endpoint's SETUP may be sent before the peer's SETUP is received, the
sender MUST handle registration failures of this kind by purging any
Token Aliases that failed to register based on the peer's
MAX_AUTH_TOKEN_CACHE_SIZE option in SETUP (or the default value of
0).
9.4.1.5. MOQT IMPLEMENTATION
The MOQT_IMPLEMENTATION option (Option Type 0x07) identifies the name
and version of the sender's MOQT implementation. This SHOULD be a
UTF-8 encoded string [RFC3629], though the message does not carry
information, such as language tags, that would aid comprehension by
any entity other than the one that created the text.
Nandakumar, et al. Expires 3 September 2026 [Page 58]
Internet-Draft moq-transport March 2026
An endpoint SHOULD send a MOQT_IMPLEMENTATION option unless
specifically configured not to do so. This option helps identify the
scope of interoperability problems and work around implementation-
specific limitations.
Senders SHOULD limit the value to the implementation name and
version, avoiding advertising or other nonessential information.
Implementations SHOULD NOT use the identifiers of other
implementations to declare compatibility, as this undermines the
usefulness of implementation identification for debugging.
9.5. GOAWAY
An endpoint sends a GOAWAY message to inform the peer it intends to
close the session soon. When sent by a server, it can initiate
session migration (Section 3.6) with an optional URI. When sent by a
client, the New Session URI MUST be zero length.
The GOAWAY message does not impact subscription state. A subscriber
SHOULD individually UNSUBSCRIBE for each existing subscription, while
a publisher MAY reject new requests after sending a GOAWAY.
Upon receiving a GOAWAY, an endpoint SHOULD NOT initiate new requests
to the peer including SUBSCRIBE, PUBLISH, FETCH, PUBLISH_NAMESPACE,
SUBSCRIBE_NAMESPACE and TRACK_STATUS.
Sending a GOAWAY does not prevent the sender from initiating new
requests, though the sender SHOULD avoid initiating requests unless
required by migration (see (Section 8.4.1 and Section 8.5.1). An
endpoint that receives a GOAWAY MAY reject new requests with an
appropriate error code (e.g., REQUEST_ERROR with error code
GOING_AWAY).
The endpoint MUST close the session with a PROTOCOL_VIOLATION
(Section 3.5) if it receives multiple GOAWAY messages.
GOAWAY Message {
Type (vi64) = 0x10,
Length (16),
New Session URI Length (vi64),
New Session URI (..),
Timeout (vi64),
}
Figure 7: MOQT GOAWAY Message
Nandakumar, et al. Expires 3 September 2026 [Page 59]
Internet-Draft moq-transport March 2026
* New Session URI: When received by a client, indicates where the
client can connect to continue this session. The client MUST use
this URI for the new session if provided. If the URI is zero
bytes long, the current URI is reused instead. The new session
URI SHOULD use the same scheme as the current URI to ensure
compatibility. The maximum length of the New Session URI is 8,192
bytes. If an endpoint receives a length exceeding the maximum, it
MUST close the session with a PROTOCOL_VIOLATION.
If a server receives a GOAWAY with a non-zero New Session URI
Length it MUST close the session with a PROTOCOL_VIOLATION.
* Timeout: The time in milliseconds the sender will wait for the
session to be gracefully closed before closing the session with
GOAWAY_TIMEOUT. A value of 0 indicates the sender has no specific
timeout, and the recipient SHOULD still close the session as
quickly as possible. This is a hint; the sender of the GOAWAY MAY
close the session before the indicated timeout has elapsed.
9.6. REQUEST_OK
The REQUEST_OK message is sent to a response to REQUEST_UPDATE,
TRACK_STATUS, SUBSCRIBE_NAMESPACE and PUBLISH_NAMESPACE requests.
REQUEST_OK Message {
Type (vi64) = 0x7,
Length (16),
Number of Parameters (vi64),
Parameters (..) ...
}
Figure 8: MOQT REQUEST_OK Message
* Parameters: The parameters are defined in Section 9.3.
9.7. REQUEST_ERROR
The REQUEST_ERROR message is sent to a response to any request
(SUBSCRIBE, FETCH, PUBLISH, SUBSCRIBE_NAMESPACE, PUBLISH_NAMESPACE,
TRACK_STATUS, REQUEST_UPDATE).
REQUEST_ERROR Message {
Type (vi64) = 0x5,
Length (16),
Error Code (vi64),
Retry Interval (vi64),
Error Reason (Reason Phrase),
}
Nandakumar, et al. Expires 3 September 2026 [Page 60]
Internet-Draft moq-transport March 2026
Figure 9: MOQT REQUEST_ERROR Message
* Error Code: Identifies an integer error code for request failure.
* Retry Interval: The minimum time (in milliseconds) before the
request SHOULD be sent again, plus one. If the value is 0, the
request SHOULD NOT be retried.
* Error Reason: Provides a text description of the request error.
See Section 1.4.4.
The application SHOULD use a relevant error code in REQUEST_ERROR, as
defined below and assigned in Section 14.5.2. Most codepoints have
identical meanings for various request types, but some have request-
specific meanings.
If a request is retryable with the same parameters at a later time,
the sender of REQUEST_ERROR includes a non-zero Retry Interval in the
message. To minimize the risk of synchronized retry storms, the
sender can apply randomization to each retry interval so that retries
are spread out over time. A Retry Interval value of 1 indicates the
request can be retried immediately.
INTERNAL_ERROR: An implementation specific or generic error
occurred.
UNAUTHORIZED: The subscriber is not authorized to perform the
requested action on the given track. This might be retryable if
the authorization token is not yet valid.
TIMEOUT: The subscription could not be completed before an
implementation specific timeout. For example, a relay could not
establish an upstream subscription within the timeout.
NOT_SUPPORTED: The endpoint does not support the type of request.
MALFORMED_AUTH_TOKEN: Invalid Auth Token serialization during
registration (see Section 9.3.2).
EXPIRED_AUTH_TOKEN: Authorization token has expired (Section 9.3.2).
GOING_AWAY: The endpoint has received a GOAWAY and MAY reject new
requests.
EXCESSIVE_LOAD: The responder is overloaded and cannot process the
request at this time. The sender SHOULD use the Retry Interval to
indicate when the request can be retried.
Nandakumar, et al. Expires 3 September 2026 [Page 61]
Internet-Draft moq-transport March 2026
DUPLICATE_SUBSCRIPTION (0x19): The PUBLISH or SUBSCRIBE request
attempted to create a subscription to a Track with the same role
as an existing subscription.
Below are errors for use by the publisher. They can appear in
response to SUBSCRIBE, FETCH, TRACK_STATUS, and SUBSCRIBE_NAMESPACE,
unless otherwise noted.
DOES_NOT_EXIST: The track or namespace is not available at the
publisher.
INVALID_RANGE: In response to SUBSCRIBE or FETCH, specified Filter
or range of Locations cannot be satisfied.
MALFORMED_TRACK: In response to a FETCH, a relay publisher detected
the track was malformed (see Section 2.4.2).
The following are errors for use by the subscriber. They can appear
in response to PUBLISH or PUBLISH_NAMESPACE, unless otherwise noted.
UNINTERESTED: The subscriber is not interested in the track or
namespace.
Errors below can only be used in response to one message type.
PREFIX_OVERLAP: In response to SUBSCRIBE_NAMESPACE, the namespace
prefix overlaps with another SUBSCRIBE_NAMESPACE in the same
session.
NAMESPACE_TOO_LARGE: In response to SUBSCRIBE_NAMESPACE, the
namespace prefix matches more publishers than the relay is willing
to enumerate.
INVALID_JOINING_REQUEST_ID: In response to a Joining FETCH, the
referenced Request ID is not an Established Subscription.
9.8. SUBSCRIBE
A subscription causes the publisher to send newly published objects
for a track.
Subscribe only requests newly published or received Objects. Objects
from the past are retrieved using FETCH (Section 9.14).
The format of SUBSCRIBE is as follows:
Nandakumar, et al. Expires 3 September 2026 [Page 62]
Internet-Draft moq-transport March 2026
SUBSCRIBE Message {
Type (vi64) = 0x3,
Length (16),
Request ID (vi64),
Required Request ID Delta (vi64),
Track Namespace (..),
Track Name Length (vi64),
Track Name (..),
Number of Parameters (vi64),
Parameters (..) ...
}
Figure 10: MOQT SUBSCRIBE Message
* Request ID: See Section 9.1.
* Required Request ID Delta: See Section 9.2.
* Track Namespace: Identifies the namespace of the track as defined
in (Section 2.4.1).
* Track Name: Identifies the track name as defined in
(Section 2.4.1).
* Parameters: The parameters are defined in Section 9.3.
On successful subscription, the publisher MUST reply with a
SUBSCRIBE_OK, allowing the subscriber to determine the start group/
object when not explicitly specified, and start sending objects.
If the publisher cannot satisfy the requested Subscription Filter
(see Section 9.3.7) or if the entire End Group has already been
published it SHOULD send a REQUEST_ERROR with code INVALID_RANGE. A
publisher MUST NOT send objects from outside the requested range.
Subscribing with the FORWARD parameter (Section 9.3.10) equal to 0
allows publisher or relay to prepare to serve the subscription in
advance, reducing the time to receive objects in the future.
9.9. SUBSCRIBE_OK
A publisher sends a SUBSCRIBE_OK as the first response message on the
bidi stream for successful subscriptions.
Nandakumar, et al. Expires 3 September 2026 [Page 63]
Internet-Draft moq-transport March 2026
SUBSCRIBE_OK Message {
Type (vi64) = 0x4,
Length (16),
Track Alias (vi64),
Number of Parameters (vi64),
Parameters (..) ...,
Track Properties (..),
}
Figure 11: MOQT SUBSCRIBE_OK Message
* Track Alias: The identifer used for this track in Subgroups or
Datagrams (see Section 10.1). The same Track Alias MUST NOT be
used by a publisher to refer to two different Tracks
simultaneously in the same session. If a subscriber receives a
SUBSCRIBE_OK that uses the same Track Alias as a different track
with an Established subscription, it MUST close the session with
error DUPLICATE_TRACK_ALIAS.
* Parameters: The parameters are defined in Section 9.3.
* Track Properties : A sequence of Properties. See Section 2.5.
9.10. REQUEST_UPDATE
The sender of a request (SUBSCRIBE, PUBLISH, FETCH,
PUBLISH_NAMESPACE, SUBSCRIBE_NAMESPACE) can later send a
REQUEST_UPDATE on the same bidi stream as the request to modify it.
A subscriber can also send REQUEST_UPDATE to modify parameters of a
subscription established with PUBLISH.
The receiver of a REQUEST_UPDATE MUST respond with exactly one
REQUEST_OK or REQUEST_ERROR message indicating if the update was
successful.
If a parameter previously set on the request is not present in
REQUEST_UPDATE, its value remains unchanged.
There is no mechanism to remove a parameter from a request.
The format of REQUEST_UPDATE is as follows:
Nandakumar, et al. Expires 3 September 2026 [Page 64]
Internet-Draft moq-transport March 2026
REQUEST_UPDATE Message {
Type (vi64) = 0x2,
Length (16),
Request ID (vi64),
Required Request ID Delta (vi64),
Number of Parameters (vi64),
Parameters (..) ...
}
Figure 12: MOQT REQUEST_UPDATE Message
* Request ID: See Section 9.1.
* Required Request ID Delta: See Section 9.2.
* Parameters: The parameters are defined in Section 9.3.
9.10.1. Updating Subscriptions
When a subscriber decreases the Start Location of the Subscription
Filter (see Section 5.1.2), the Start Location can be smaller than
the Track's Largest Location, similar to a new Subscription. FETCH
can be used to retrieve any necessary Objects smaller than the
current Largest Location.
When a subscriber increases the End Location, the Largest Object at
the publisher might already be larger than the previous End Location.
This will create a gap in the subscription. The REQUEST_OK in
response to the REQUEST_UPDATE will include the LARGEST_OBJECT
parameter, and the subscriber can issue a FETCH to retrieve the
omitted Objects, if any.
When a subscriber narrows their subscription (increase the Start
Location and/or decrease the End Group), it might still receive
Objects outside the new range if the publisher sent them before the
update was processed.
When a subscription update is unsuccessful, the publisher MUST also
terminate the subscription with PUBLISH_DONE with error code
UPDATE_FAILED.
9.11. PUBLISH
The publisher sends PUBLISH as the first message on a new
bidirectional stream to initiate a subscription for a Track. The
receiver verifies the publisher is authorized to publish this track.
Nandakumar, et al. Expires 3 September 2026 [Page 65]
Internet-Draft moq-transport March 2026
PUBLISH Message {
Type (vi64) = 0x1D,
Length (16),
Request ID (vi64),
Required Request ID Delta (vi64),
Track Namespace (..),
Track Name Length (vi64),
Track Name (..),
Track Alias (vi64),
Number of Parameters (vi64),
Parameters (..) ...,
Track Properties (..),
}
Figure 13: MOQT PUBLISH Message
* Request ID: See Section 9.1.
* Required Request ID Delta: See Section 9.2.
* Track Namespace: Identifies a track's namespace as defined in
(Section 2.4.1)
* Track Name: Identifies the track name as defined in
(Section 2.4.1).
* Track Alias: The identifer used for this track in Subgroups or
Datagrams (see Section 10.1). The same Track Alias MUST NOT be
used by a publisher to refer to two different Tracks
simultaneously in the same session. If a subscriber receives a
PUBLISH that uses the same Track Alias as a different track with
an Established subscription, it MUST close the session with error
DUPLICATE_TRACK_ALIAS.
* Parameters: The parameters are defined in Section 9.3.
* Track Properties : A sequence of Properties. See Section 2.5.
A subscriber receiving a PUBLISH for a Track it does not wish to
receive SHOULD send REQUEST_ERROR with error code UNINTERESTED, and
abandon reading any publisher initiated streams associated with that
subscription using a STOP_SENDING frame.
A publisher that sends the FORWARD parameter (Section 9.3.10) equal
to 0 indicates that it will not transmit any objects until the
subscriber sets the Forward State to 1. If the FORWARD parameter is
omitted or equal to 1, the publisher will start transmitting objects
immediately, possibly before PUBLISH_OK.
Nandakumar, et al. Expires 3 September 2026 [Page 66]
Internet-Draft moq-transport March 2026
9.12. PUBLISH_OK
The subscriber sends a PUBLISH_OK as the first response message on
the bidi stream to acknowledge the successful authorization and
acceptance of a PUBLISH message, and establish a subscription.
PUBLISH_OK Message {
Type (vi64) = 0x1E,
Length (16),
Number of Parameters (vi64),
Parameters (..) ...,
}
Figure 14: MOQT PUBLISH_OK Message
* Parameters: The parameters are defined in Section 9.3.
TODO: A similar section to SUBSCRIBE about how the publisher handles
a filter that is entirely behind Largest Object or is otherwise
invalid.
9.13. PUBLISH_DONE
A publisher sends a PUBLISH_DONE message as the final message before
closing the subscription's bidi stream to indicate it is done
publishing Objects for that subscription. The Status Code indicates
why the subscription ended, and whether it was an error. Because
PUBLISH_DONE is sent on the control stream, it is likely to arrive at
the receiver before late-arriving objects, and often even late-
opening streams. However, the receiver uses it as an indication that
it should receive any late-opening streams in a relatively short
time.
Note that some objects in the subscribed track might never be
delivered, because a stream was reset, or never opened in the first
place, due to the delivery timeout.
A sender MUST NOT send PUBLISH_DONE until it has closed all streams
it will ever open, and has no further datagrams to send, for a
subscription. After sending PUBLISH_DONE, the sender can immediately
destroy subscription state, although stream state can persist until
delivery completes. The sender might persist subscription state to
enforce the delivery timeout by resetting streams on which it has
already sent FIN, only deleting it when all such streams have
received ACK of the FIN.
Nandakumar, et al. Expires 3 September 2026 [Page 67]
Internet-Draft moq-transport March 2026
A sender MUST NOT destroy subscription state until it sends
PUBLISH_DONE, though it can choose to stop sending objects (and thus
send PUBLISH_DONE) for any reason.
A subscriber that receives PUBLISH_DONE SHOULD set a timer of at
least its delivery timeout in case some objects are still inbound due
to prioritization or packet loss. The subscriber MAY dispense with a
timer if it unsubscribed or is otherwise no longer interested in
objects from the track. Once the timer has expired, the receiver
destroys subscription state once all open streams for the
subscription have closed. A subscriber MAY discard subscription
state earlier, at the cost of potentially not delivering some late
objects to the application. The subscriber SHOULD send STOP_SENDING
on all streams related to the subscription when it deletes
subscription state.
The format of PUBLISH_DONE is as follows:
PUBLISH_DONE Message {
Type (vi64) = 0xB,
Length (16),
Status Code (vi64),
Stream Count (vi64),
Error Reason (Reason Phrase)
}
Figure 15: MOQT PUBLISH_DONE Message
* Status Code: An integer status code indicating why the
subscription ended.
* Stream Count: An integer indicating the number of data streams the
publisher opened for this subscription, including streams that
contained no Objects (e.g., an empty Subgroup). This helps the
subscriber know if it has received all of the data published in
this subscription by comparing the number of streams received.
The subscriber can immediately remove all subscription state once
the same number of streams have been processed. If the publisher
did not open any streams for this subscription, the publisher MUST
set Stream Count to 0. If the publisher is unable to set Stream
Count to the exact number of streams opened for the subscription,
it MUST set Stream Count to 2^62 - 1. Subscribers SHOULD use a
timeout or other mechanism to remove subscription state in case
the publisher set an incorrect value, reset a stream before the
SUBGROUP_HEADER, or set the maximum value. If a subscriber
receives more streams for a subscription than specified in Stream
Count, it MAY close the session with a PROTOCOL_VIOLATION.
Nandakumar, et al. Expires 3 September 2026 [Page 68]
Internet-Draft moq-transport March 2026
* Error Reason: Provides the reason for subscription error. See
Section 1.4.4.
The application SHOULD use a relevant status code in PUBLISH_DONE, as
defined below:
INTERNAL_ERROR (0x0): An implementation specific or generic error
occurred.
UNAUTHORIZED (0x1): The subscriber is no longer authorized to
subscribe to the given track.
TRACK_ENDED (0x2): The track is no longer being published.
SUBSCRIPTION_ENDED (0x3): The publisher reached the end of an
associated subscription filter.
GOING_AWAY (0x4): The subscriber or publisher issued a GOAWAY
message.
EXPIRED (0x5): The publisher reached the timeout specified in
SUBSCRIBE_OK.
TOO_FAR_BEHIND (0x6): The publisher's queue of objects to be sent to
the given subscriber exceeds its implementation defined limit.
MALFORMED_TRACK (0x12): A relay publisher detected that the track
was malformed (see Section 2.4.2).
UPDATE_FAILED (0x8): REQUEST_UPDATE failed on this subscription (see
Section 9.10).
EXCESSIVE_LOAD (0x9): The publisher is overloaded and is terminating
the subscription.
9.14. FETCH
A subscriber sends FETCH as the first message on a new bidi stream to
a publisher to request a range of already published objects within a
track.
There are three types of Fetch messages.
Nandakumar, et al. Expires 3 September 2026 [Page 69]
Internet-Draft moq-transport March 2026
+======+========================+
| Code | Fetch Type |
+======+========================+
| 0x1 | Standalone Fetch |
+------+------------------------+
| 0x2 | Relative Joining Fetch |
+------+------------------------+
| 0x3 | Absolute Joining Fetch |
+------+------------------------+
Table 5
An endpoint that receives a Fetch Type other than 0x1, 0x2 or 0x3
MUST close the session with a PROTOCOL_VIOLATION.
9.14.1. Standalone Fetch
A Fetch of Objects performed independently of any Subscribe.
A Standalone Fetch includes this structure:
Standalone Fetch {
Track Namespace (..),
Track Name Length (vi64),
Track Name (..),
Start Location (Location),
End Location (Location)
}
* Track Namespace: Identifies the namespace of the track as defined
in (Section 2.4.1).
* Track Name: Identifies the track name as defined in
(Section 2.4.1).
* Start Location: The start Location.
* End Location: The end Location, plus 1. A Location.Object value
of 0 means the entire group is requested.
9.14.2. Joining Fetches
A Joining Fetch is associated with a Subscribe request by specifying
the Request ID of a subscription in the Established or Pending
(subscriber) state. Because Joining Fetch references an existing
subscription, if that subscription has not yet been established, the
Publisher receiving the Joining Fetch buffers the pending Joining
Fetch until either the Subscription is established or the request
Nandakumar, et al. Expires 3 September 2026 [Page 70]
Internet-Draft moq-transport March 2026
times out.
A publisher receiving a Joining Fetch uses properties of the
associated subscription to determine the Track Namespace, Track Name
and End Location such that it is contiguous with the associated
subscription. The subscriber can set the Start Location to an
absolute Location or a Location relative to the Largest group.
A Subscriber can use a Joining Fetch to, for example, fill a playback
buffer with a certain number of groups prior to the live edge of a
track.
A Joining Fetch is only permitted when the associated subscription
has Forward State 1; otherwise the publisher MUST close the session
with a PROTOCOL_VIOLATION.
If no Objects have been published for the track the publisher MUST
respond with a REQUEST_ERROR with error code INVALID_RANGE.
A Joining Fetch includes this structure:
Joining Fetch {
Joining Request ID (vi64),
Joining Start (vi64)
}
* Joining Request ID: The Request ID of the subscription to be
joined. If a publisher receives a Joining Fetch with a Request ID
that does not correspond to a subscription in the same session in
the Established or Pending (subscriber) states, it MUST return a
REQUEST_ERROR with error code INVALID_JOINING_REQUEST_ID.
* Joining Start : A relative or absolute value used to determine the
Start Location, described below.
9.14.2.1. Joining Fetch Range Calculation
The Joining Location value from the corresponding subscription is
used to calculate the end of a Joining Fetch, so the Objects
retrieved by the FETCH and SUBSCRIBE are contiguous and non-
overlapping.
The publisher receiving a Joining Fetch sets the End Location to
{Joining Location.Group, Joining Location.Object + 1} (see
Section 5.1.
Nandakumar, et al. Expires 3 September 2026 [Page 71]
Internet-Draft moq-transport March 2026
Note: the last Object included in the Joining FETCH response is the
Object at the Joining Location. The + 1 above indicates the
equivalent Standalone Fetch encoding.
For a Relative Joining Fetch, the publisher sets the Start Location
to {Joining Location.Group - Joining Start, 0}.
For an Absolute Joining Fetch, the publisher sets the Start Location
to {Joining Start, 0}.
9.14.3. Fetch Handling
The format of FETCH is as follows:
FETCH Message {
Type (vi64) = 0x16,
Length (16),
Request ID (vi64),
Required Request ID Delta (vi64),
Fetch Type (vi64),
[Standalone (Standalone Fetch),]
[Joining (Joining Fetch),]
Number of Parameters (vi64),
Parameters (..) ...
}
Figure 16: MOQT FETCH Message
* Request ID: See Section 9.1.
* Required Request ID Delta: See Section 9.2.
* Fetch Type: Identifies the type of Fetch, whether Standalone,
Relative Joining or Absolute Joining.
* Standalone: Standalone Fetch structure included when Fetch Type is
0x1
* Joining: Joining Fetch structure included when Fetch Type is 0x2
or 0x3.
* Parameters: The parameters are defined in Section 9.3.
A publisher responds to a FETCH request with either a FETCH_OK or a
REQUEST_ERROR message. The publisher creates a new unidirectional
stream that is used to send the Objects. The FETCH_OK or
REQUEST_ERROR can come at any time relative to object delivery.
Nandakumar, et al. Expires 3 September 2026 [Page 72]
Internet-Draft moq-transport March 2026
The publisher responding to a FETCH is responsible for delivering all
available Objects in the requested range in the requested order (see
Section 9.3.6). The Objects in the response are delivered on a
single unidirectional stream. Any gaps in the Group and Object IDs
in the response stream indicate objects that do not exist. For
Ascending Group Order this includes ranges between the first
requested object and the first object in the stream; between objects
in the stream; and between the last object in the stream and the
Largest Group/Object indicated in FETCH_OK, so long as the fetch
stream is terminated by a FIN. If no Objects exist in the requested
range, the publisher opens the unidirectional stream, sends the
FETCH_HEADER (see Section 10.4.4) and closes the stream with a FIN.
A relay that has cached objects from the beginning of the range MAY
start sending objects immediately in response to a FETCH. If it
encounters an object in the requested range that is not cached and
has unknown status, the relay MUST pause subsequent delivery until it
has confirmed the object's status upstream. If the upstream FETCH
fails, the relay sends a REQUEST_ERROR and can reset the
unidirectional stream. It can choose to do so immediately or wait
until the cached objects have been delivered before resetting the
stream.
The Object Forwarding Preference does not apply to fetches.
Fetch specifies an inclusive range of Objects starting at Start
Location and ending at End Location. End Location MUST specify the
same or a larger Location than Start Location for Standalone and
Absolute Joining Fetches.
Objects that are not yet published will not be retrieved by a FETCH.
The Largest available Object in the requested range is indicated in
the FETCH_OK, and is the last Object a fetch will return if the End
Location have not yet been published.
If Start Location is greater than the Largest Object (Section 9.8)
the publisher MUST return REQUEST_ERROR with error code
INVALID_RANGE.
A publisher MUST send fetched groups in the requested group order,
either ascending or descending. Within each group, objects are sent
in Object ID order; subgroup ID is not used for ordering.
Nandakumar, et al. Expires 3 September 2026 [Page 73]
Internet-Draft moq-transport March 2026
If a Publisher receives a FETCH with a range that includes one or
more Objects with unknown status (e.g. a Relay has temporarily lost
contact with the Original Publisher and does not have the Object in
cache), it can choose to reset the FETCH data stream with
UNKNOWN_OBJECT_STATUS, or indicate the range of unknown Objects and
continue serving other known Objects.
9.15. FETCH_OK
A publisher sends a FETCH_OK as the first message on the bidi stream
in response to a successful fetch. A publisher MAY send Objects in
response to a FETCH before the FETCH_OK message is sent, but the
FETCH_OK MUST NOT be sent until the End Location is known.
FETCH_OK Message {
Type (vi64) = 0x18,
Length (16),
End Of Track (8),
End Location (Location),
Number of Parameters (vi64),
Parameters (..) ...
Track Properties (..),
}
Figure 17: MOQT FETCH_OK Message
* End Of Track: 1 if all Objects have been published on this Track,
and the End Location is the final Object in the Track, 0 if not.
* End Location: The largest object covered by the FETCH response.
The End Location is determined as follows:
- If the requested FETCH End Location was beyond the Largest
known (possibly final) Object, End Location is {Largest.Group,
Largest.Object + 1}
- If End Location.Object in the FETCH request was 0 and the
response covers the last Object in the Group, End Location is
{Fetch.End Location.Group, 0}
- Otherwise, End Location is Fetch.End Location Where Fetch.End
Location is either Fetch.Standalone.End Location or the
computed End Location described in Section 9.14.2.1.
Nandakumar, et al. Expires 3 September 2026 [Page 74]
Internet-Draft moq-transport March 2026
If the relay is subscribed to the track, it uses its knowledge of
the largest {Group, Object} to set End Location. If it is not
subscribed and the requested End Location exceeds its cached data,
the relay makes an upstream request to complete the FETCH, and
uses the upstream response to set End Location.
If End Location is smaller than the Start Location in the
corresponding FETCH the receiver MUST close the session with a
PROTOCOL_VIOLATION.
* Parameters: The parameters are defined in Section 9.3.
* Track Properties : A sequence of Properties. See Section 2.5.
9.16. TRACK_STATUS
A potential subscriber sends TRACK_STATUS as the first and only
message on a new bidi stream to obtain information about the current
status of a given track.
The TRACK_STATUS message format is identical to the SUBSCRIBE message
(Section 9.8), but subscriber parameters related to Track delivery
(e.g. SUBSCRIBER_PRIORITY) are not included.
The receiver of a TRACK_STATUS message treats it identically as if it
had received a SUBSCRIBE message, except it does not create
downstream subscription state or send any Objects. If successful,
the publisher responds with a REQUEST_OK message with the same
parameters it would have set in a SUBSCRIBE_OK. Track Alias is not
used. A publisher responds to a failed TRACK_STATUS with an
appropriate REQUEST_ERROR message. The bidi stream is closed with a
FIN after REQUEST_OK or REQUEST_ERROR are sent.
Relays without an Established subscription MAY forward TRACK_STATUS
to one or more publishers, or MAY initiate a subscription (subject to
authorization) as described in Section 8.5 to determine the response.
The publisher does not send PUBLISH_DONE for this request, and the
subscriber cannot send REQUEST_UPDATE.
9.17. PUBLISH_NAMESPACE
The publisher sends the PUBLISH_NAMESPACE message as the first
message on a new bidi stream to advertise that it has tracks
available within a Track Namespace. The receiver verifies the
publisher is authorized to publish tracks under this namespace.
Nandakumar, et al. Expires 3 September 2026 [Page 75]
Internet-Draft moq-transport March 2026
PUBLISH_NAMESPACE Message {
Type (vi64) = 0x6,
Length (16),
Request ID (vi64),
Required Request ID Delta (vi64),
Track Namespace (..),
Number of Parameters (vi64),
Parameters (..) ...
}
Figure 18: MOQT PUBLISH_NAMESPACE Message
* Request ID: See Section 9.1.
* Required Request ID Delta: See Section 9.2.
* Track Namespace: Identifies a track's namespace as defined in
Section 2.4.1.
* Parameters: The parameters are defined in Section 9.3.
9.18. NAMESPACE
The NAMESPACE message is similar to the PUBLISH_NAMESPACE message,
except it is sent on the response stream of a SUBSCRIBE_NAMESPACE
request. All NAMESPACE messages are in response to a
SUBSCRIBE_NAMESPACE, so only the namespace tuples after the 'Track
Namespace Prefix' are included in the 'Track Namespace Suffix'.
NAMESPACE Message {
Type (i) = 0x8,
Length (16),
Track Namespace Suffix (..),
}
Figure 19: MOQT NAMESPACE Message
* Track Namespace Suffix: Specifies the final portion of a track's
namespace as defined in Section 2.4.1 after removing namespace
tuples included in 'Track Namespace Prefix' {message-subscribe-
ns}.
Nandakumar, et al. Expires 3 September 2026 [Page 76]
Internet-Draft moq-transport March 2026
9.19. NAMESPACE_DONE
The publisher sends the NAMESPACE_DONE control message to indicate
its intent to stop serving new subscriptions for tracks within the
provided Track Namespace. All NAMESPACE_DONE messages are in
response to a SUBSCRIBE_NAMESPACE, so only the namespace tuples after
the 'Track Namespace Prefix' are included in the 'Track Namespace
Suffix'.
NAMESPACE_DONE Message {
Type (i) = 0xE,
Length (16),
Track Namespace Suffix (..)
}
Figure 20: MOQT NAMESPACE_DONE Message
* Track Namespace Suffix: Specifies the final portion of a track's
namespace as defined in Section 2.4.1. The namespace begins with
the 'Track Namespace Prefix' specified in {message-subscribe-ns}.
9.20. SUBSCRIBE_NAMESPACE
The subscriber sends a SUBSCRIBE_NAMESPACE control message on a new
bidirectional stream to a publisher to request the current set of
matching published namespaces and/or Established subscriptions, as
well as future updates to the set.
SUBSCRIBE_NAMESPACE Message {
Type (vi64) = 0x11,
Length (16),
Request ID (vi64),
Required Request ID Delta (vi64),
Track Namespace Prefix (..),
Subscribe Options (vi64),
Number of Parameters (vi64),
Parameters (..) ...
}
Figure 21: MOQT SUBSCRIBE_NAMESPACE Message
* Request ID: See Section 9.1.
* Required Request ID Delta: See Section 9.2.
* Track Namespace Prefix: A Track Namespace structure as described
in Section 2.4.1 with between 0 and 32 Track Namespace Fields.
This prefix is matched against track namespaces known to the
Nandakumar, et al. Expires 3 September 2026 [Page 77]
Internet-Draft moq-transport March 2026
publisher. For example, if the publisher is a relay that has
received PUBLISH_NAMESPACE messages for namespaces ("example.com",
"meeting=123", "participant=100") and ("example.com",
"meeting=123", "participant=200"), a SUBSCRIBE_NAMESPACE for
("example.com", "meeting=123") would match both. If an endpoint
receives a Track Namespace Prefix consisting of greater than than
32 Track Namespace Fields, it MUST close the session with a
PROTOCOL_VIOLATION.
* Subscribe Options: Allows subscribers to request PUBLISH (0x00),
NAMESPACE (0x01), or both (0x02) for a given SUBSCRIBE_NAMESPACE
request.
* Parameters: The parameters are defined in Section 9.3.
The publisher will respond with REQUEST_OK or REQUEST_ERROR on the
response half of the stream. If the subscriber receives any frame
other than a REQUEST_OK or a REQUEST_ERROR as the first frame on the
response half of the stream, then it MUST close the session with a
PROTOCOL_VIOLATION. If the SUBSCRIBE_NAMESPACE is successful, the
publisher will send matching NAMESPACE messages on the response
stream if they are requested. If it is an error, the stream will be
immediately closed via FIN. Also, any matching PUBLISH messages
without an Established Subscription will be established on new
bidirectional streams. When there are changes to the namespaces or
subscriptions being published and the subscriber is subscribed to
them, the publisher sends the corresponding NAMESPACE,
NAMESPACE_DONE, or PUBLISH messages.
A subscriber cannot make overlapping namespace subscriptions on a
single session. Within a session, if a publisher receives a
SUBSCRIBE_NAMESPACE with a Track Namespace Prefix that shares a
common prefix with an established namespace subscription, it MUST
respond with REQUEST_ERROR with error code PREFIX_OVERLAP.
The publisher MUST ensure the subscriber is authorized to perform
this namespace subscription.
SUBSCRIBE_NAMESPACE is not required for a publisher to send
PUBLISH_NAMESPACE or PUBLISH messages to a subscriber. It is useful
in applications or relays where subscribers are only interested in or
authorized to access a subset of available namespaces and tracks.
Nandakumar, et al. Expires 3 September 2026 [Page 78]
Internet-Draft moq-transport March 2026
If the FORWARD parameter (Section 9.3.10) is present in this message
and equal to 0, PUBLISH messages resulting from this
SUBSCRIBE_NAMESPACE will set the FORWARD parameter to 0. If the
FORWARD parameter is equal to 1 or omitted from this message, PUBLISH
messages resulting from this SUBSCRIBE_NAMESPACE will set the FORWARD
parameter to 1, or indicate that value by omitting the parameter (see
Section 5.1).
The publisher MUST NOT send NAMESPACE_DONE for a namespace suffix
before the corresponding NAMESPACE. If a subscriber receives a
NAMESPACE_DONE before the corresponding NAMESPACE, it MUST close the
session with a 'PROTOCOL_VIOLATION'.
If the publisher is unable to send NAMESPACE or NAMESPACE_DONE
messages in a timely manner because the SUBSCRIBE_NAMESPACE response
stream is blocked by flow control, the publisher MAY reset the
SUBSCRIBE_NAMESPACE response stream. When a subscriber receives a
stream reset on a SUBSCRIBE_NAMESPACE response stream, it SHOULD
treat this as though each active namespace received a NAMESPACE_DONE.
9.21. PUBLISH_BLOCKED
The publisher sends the PUBLISH_BLOCKED control message to indicate
it cannot send a PUBLISH message to initiate a new Subscription for a
Track in the SUBSCRIBE_NAMESPACE's Track Namespace. All
PUBLISH_BLOCKED messages are in response to a SUBSCRIBE_NAMESPACE, so
only the namespace tuples after the 'Track Namespace Prefix' are
included in the 'Track Namespace Suffix'.
PUBLISH_BLOCKED Message {
Type (vi64) = 0xF,
Length (16),
Track Namespace Suffix (..),
Track Name Length (vi64),
Track Name (..),
}
Figure 22: MOQT PUBLISH_BLOCKED Message
* Track Namespace Suffix: Specifies the final portion of a track's
namespace as defined in Section 2.4.1. The namespace begins with
the 'Track Namespace Prefix' specified in {message-subscribe-ns}.
* Track Name: Identifies the track name as defined in
(Section 2.4.1).
Nandakumar, et al. Expires 3 September 2026 [Page 79]
Internet-Draft moq-transport March 2026
10. Data Streams and Datagrams
A publisher sends Objects matching a subscription on Data Streams or
Datagrams and sends Objects matching a FETCH request on one Data
Stream.
Unidirectional stream types are defined in Section 3.4. Data streams
use SUBGROUP_HEADER or FETCH_HEADER types.
All MOQT datagrams start with a variable-length integer indicating
the type of the datagram. See Section 10.3.1.
An endpoint that receives an unknown datagram type MUST close the
session.
Every Object has a 'Object Forwarding Preference' and the Original
Publisher MAY use both Subgroups and Datagrams within a Group or
Track.
10.1. Track Alias
To optimize wire efficiency, Subgroups and Datagrams refer to a track
by a numeric identifier, rather than the Full Track Name. Track
Alias is chosen by the publisher and included in SUBSCRIBE_OK
(Section 9.9) or PUBLISH (Section 9.11).
Objects can arrive after a subscription has been cancelled.
Subscribers SHOULD retain sufficient state to quickly discard these
unwanted Objects, rather than treating them as belonging to an
unknown Track Alias.
10.2. Objects
An Object contains a range of contiguous bytes from the specified
track, as well as associated metadata required to deliver, cache, and
forward it. Objects are sent by publishers.
10.2.1. Object Header
A canonical MoQ Object has the following fields:
* Track Namespace and Track Name: The track this object belongs to.
* Group ID: The identifier of the Object's Group (see Section 2.3)
within the Track.
* Object ID: The order of the object within the group.
Nandakumar, et al. Expires 3 September 2026 [Page 80]
Internet-Draft moq-transport March 2026
* Publisher Priority: An 8 bit integer indicating the publisher's
priority for the Object (Section 7).
* Object Forwarding Preference: An enumeration indicating how a
publisher sends an object. The preferences are Subgroup and
Datagram. Object Forwarding Preference is a property of an
individual Object and can vary among Objects in the same Track.
In a subscription, an Object MUST be sent according to its Object
Forwarding Preference.
* Subgroup ID: The identifier of the Object's Subgroup (see
Section 2.2) within the Group. This field is omitted if the
Object Forwarding Preference is Datagram.
* Object Status: An enumeration used to indicate whether the Object
is a normal Object or mark the end of a group or track. See
Section 10.2.1.1 below.
* Object Properties : A sequence of Properties associated with the
object. See Section 10.2.1.2.
* Object Payload: An opaque payload intended for an End Subscriber
and SHOULD NOT be processed by a relay. Only present when 'Object
Status' is Normal (0x0).
10.2.1.1. Object Status
The Object Status is a field that is only present in objects that are
delivered via a SUBSCRIPTION, and is absent in Objects delivered via
a FETCH. It allows the publisher to explicitly communicate that a
specific range of objects does not exist.
Status can have following values:
* 0x0 := Normal object. This status is implicit for any non-zero
length object. Zero-length objects explicitly encode the Normal
status.
* 0x3 := Indicates End of Group. Indicates that no objects with the
specified Group ID and the Object ID that is greater than or equal
to the one specified exist in the group identified by the Group
ID.
* 0x4 := Indicates End of Track. Indicates that no objects with the
location that is equal to or greater than the one specified exist.
All of those SHOULD be cached.
Nandakumar, et al. Expires 3 September 2026 [Page 81]
Internet-Draft moq-transport March 2026
Any other value SHOULD be treated as a protocol error and the session
SHOULD be closed with a PROTOCOL_VIOLATION (Section 3.5). Any object
with a status code other than zero MUST have an empty payload.
10.2.1.2. Object Properties
Any Object with status Normal can have properties (Section 2.5). If
an endpoint receives properties on an Object with status that is not
Normal, it MUST close the session with a PROTOCOL_VIOLATION.
Object Properties are visible to relays and are intended to be
relevant to MOQT Object distribution. Any Object metadata never
intended to be accessed by the transport or Relays SHOULD be
serialized as part of the Object payload and not as an Object
Property.
Object Properties are serialized as a length in bytes followed by
Key-Value-Pairs (see Figure 2).
Object Properties {
Properties Length (vi64),
Properties (..),
}
Object Property types are registered in the IANA table 'MOQ
Properties'. See Section 14.
10.3. Datagrams
A single object can be conveyed in a datagram. The Track Alias field
(Section 10.1) indicates the track this Datagram belongs to. If an
endpoint receives a datagram with an unknown Track Alias, it MAY drop
the datagram or choose to buffer it for a brief period to handle
reordering with the control message that establishes the Track Alias.
An Object received in an OBJECT_DATAGRAM message has an Object
Forwarding Preference = Datagram.
To send an Object with Object Forwarding Preference = Datagram,
determine the length of the header and payload and send the Object as
datagram. When the total size is larger than the maximum datagram
size for the session, the Object will be dropped without any explicit
notification.
Nandakumar, et al. Expires 3 September 2026 [Page 82]
Internet-Draft moq-transport March 2026
Each session along the path between the Original Publisher and End
Subscriber might have different maximum datagram sizes.
Additionally, Object Properties (Section 10.2.1.2) can be added to
Objects as they pass through the MOQT network, increasing the size of
the Object and the chances it will exceed the maximum datagram size
of a downstream session and be dropped.
10.3.1. Object Datagram
An OBJECT_DATAGRAM carries a single object in a datagram.
OBJECT_DATAGRAM {
Type (i) = 0x00..0x0F / 0x20..0x21 / 0x24..0x25 /
0x28..0x29 / 0x2C..0x2D,
Track Alias (vi64),
Group ID (vi64),
[Object ID (vi64),]
[Publisher Priority (8),]
[Properties (..),]
[Object Status (vi64),]
[Object Payload (..),]
}
Figure 23: MOQT OBJECT_DATAGRAM
The Type field in the OBJECT_DATAGRAM takes the form 0b00X0XXXX (or
the set of values from 0x00 to 0x0F, 0x20 to 0x2F). However, not all
Type values in this range are valid. The four low-order bits and bit
5 of the Type field determine which fields are present in the
datagram:
* The *PROPERTIES* bit (0x01) indicates when the Properties field is
present. When set to 1, the Object Properties structure defined
in Section 10.2.1.2 is present. When set to 0, the field is
absent. If an endpoint receives a datagram with the PROPERTIES
bit set and an Properties Length of 0, it MUST close the session
with a PROTOCOL_VIOLATION.
* The *END_OF_GROUP* bit (0x02) indicates End of Group. When set to
1, this indicates that no Object with the same Group ID and an
Object ID greater than the Object ID in this datagram exists.
* The *ZERO_OBJECT_ID* bit (0x04) indicates when the Object ID field
is present. When set to 1, the Object ID field is omitted and the
Object ID is
1. When set to 0, the Object ID field is present.
Nandakumar, et al. Expires 3 September 2026 [Page 83]
Internet-Draft moq-transport March 2026
* The *DEFAULT_PRIORITY* bit (0x08) indicates when the Priority
field is present. When set to 1, the Priority field is omitted
and this Object inherits the Publisher Priority specified in the
control message that established the subscription. When set to 0,
the Priority field is present.
* The *STATUS* bit (0x20) indicates whether the datagram contains an
Object Status or Object Payload. When set to 1, the Object Status
field is present and there is no Object Payload. When set to 0,
the Object Payload is present and the Object Status field is
omitted. There is no explicit length field for the Object
Payload; the entirety of the transport datagram following the
Object header contains the payload.
The following Type values are invalid. If an endpoint receives a
datagram with any of these Type values, it MUST close the session
with a PROTOCOL_VIOLATION:
* Type values with both the STATUS bit (0x20) and END_OF_GROUP bit
(0x02) set: 0x22, 0x23, 0x26, 0x27, 0x2A, 0x2B, 0x2E, 0x2F. An
object status message cannot signal end of group.
* Type values that do not match the form 0b00X0XXXX (i.e., Type
values outside the ranges 0x00..0x0F and 0x20..0x2F).
If an Object Datagram includes both the STATUS bit and PROPERTIES
bit, and the Object Status is not Normal (0x0), the endpoint MUST
close the session with a PROTOCOL_VIOLATION, because only Normal
Objects can have Properties.
10.4. Streams
When Objects are sent on streams, the stream begins with a Subgroup
or Fetch Header and is followed by one or more sets of serialized
Object fields. If a stream ends gracefully (i.e., the stream
terminates with a FIN) in the middle of a serialized Object, the
session SHOULD be closed with a PROTOCOL_VIOLATION.
A publisher SHOULD NOT open more than one stream at a time with the
same Subgroup Header field values.
Nandakumar, et al. Expires 3 September 2026 [Page 84]
Internet-Draft moq-transport March 2026
10.4.1. Stream Cancellation
Streams aside from the control streams MAY be canceled due to
congestion or other reasons by either the publisher or subscriber.
Early termination of a unidirectional stream does not affect the MoQ
application state, and therefore has no effect on outstanding
subscriptions. Termination of a bidi request stream terminates the
Subscription, Fetch, Track Status, Publish Namespace, or Subscribe
Namespace request. When possible, Publishers SHOULD send a
PUBLISH_DONE when terminating a subscription instead of abruptly
terminating the associated control stream.
10.4.2. Subgroup Header
All Objects on a Subgroup stream belong to the track identified by
Track Alias (see Section 10.1) and the Subgroup indicated by 'Group
ID' and Subgroup ID indicated by the SUBGROUP_HEADER.
If an endpoint receives a subgroup with an unknown Track Alias, it
MAY abandon the stream, or choose to buffer it for a brief period to
handle reordering with the control message that establishes the Track
Alias. The endpoint MAY withhold stream flow control beyond the
SUBGROUP_HEADER until the Track Alias has been established. To
prevent deadlocks, endpoints MUST allocate connection flow control to
the control streams before allocating it to any data streams.
Otherwise, a receiver might wait for a control message containing a
Track Alias to release flow control, while the sender waits for flow
control to send the message.
SUBGROUP_HEADER {
Type (i) = 0x10..0x15 / 0x18..0x1D / 0x30..0x35 / 0x38..0x3D,
Track Alias (vi64),
Group ID (vi64),
[Subgroup ID (vi64),]
[Publisher Priority (8),]
}
Figure 24: MOQT SUBGROUP_HEADER
All Objects received on a stream opened with SUBGROUP_HEADER have an
Object Forwarding Preference = Subgroup.
The Type field in the SUBGROUP_HEADER takes the form 0b00X1XXXX (or
the set of values from 0x10 to 0x1F, 0x30 to 0x3F), where bit 4 is
always set to 1. However, not all Type values in this range are
valid. The four low-order bits and bit 5 determine which fields are
present in the header:
Nandakumar, et al. Expires 3 September 2026 [Page 85]
Internet-Draft moq-transport March 2026
* The *PROPERTIES* bit (0x01) indicates when the Properties field is
present in all Objects in this Subgroup. When set to 1, the
Object Properties structure defined in Section 10.2.1.2 is present
in all Objects. When set to 0, the field is never present.
Objects with no properties set Properties Length to 0.
* The *SUBGROUP_ID_MODE* field (bits 1-2, mask 0x06) is a two-bit
field that determines the encoding of the Subgroup ID. To extract
this value, perform a bitwise AND with mask 0x06 and right-shift
by 1 bit:
- 0b00: The Subgroup ID field is absent and the Subgroup ID is 0.
- 0b01: The Subgroup ID field is absent and the Subgroup ID is
the Object ID of the first Object transmitted in this Subgroup.
- 0b10: The Subgroup ID field is present in the header.
- 0b11: Reserved for future use.
* The *END_OF_GROUP* bit (0x08) indicates that this subgroup
contains the largest Object in the Group. When set to 1, the
subscriber can infer the final Object in the Group when the data
stream is terminated by a FIN. In this case, Objects that have
the same Group ID and an Object ID larger than the last Object
received on the stream do not exist. This does not apply when the
data stream is terminated with a RESET_STREAM or RESET_STREAM_AT.
* The *DEFAULT_PRIORITY* bit (0x20) indicates when the Priority
field is present. When set to 1, the Priority field is omitted
and this Subgroup inherits the Publisher Priority specified in the
control message that established the subscription. When set to 0,
the Priority field is present in the Subgroup header.
The following Type values are invalid. If an endpoint receives a
stream header with any of these Type values, it MUST close the
session with a PROTOCOL_VIOLATION:
* Type values with SUBGROUP_ID_MODE set to 0b11: 0x16, 0x17, 0x1E,
0x1F, 0x36, 0x37, 0x3E, 0x3F. This mode is reserved for future
use.
* Type values that do not match the form 0b00X1XXXX (i.e., Type
values outside the ranges 0x10..0x1F and 0x30..0x3F, or values
where bit 4 is not set).
Nandakumar, et al. Expires 3 September 2026 [Page 86]
Internet-Draft moq-transport March 2026
To send an Object with Object Forwarding Preference = Subgroup, find
the open stream that is associated with the subscription, Group ID
and Subgroup ID, or open a new one and send the SUBGROUP_HEADER.
Then serialize the following fields.
The Object Status field is only sent if the Object Payload Length is
zero.
The Object ID Delta + 1 is added to the previous Object ID in the
Subgroup stream if there was one. The Object ID is the Object ID
Delta if it's the first Object in the Subgroup stream. For example,
a Subgroup of sequential Object IDs starting at 0 will have 0 for all
Object ID Delta values. A consumer cannot infer information about
the existence of Objects between the current and previous Object ID
in the Subgroup (e.g. when Object ID Delta is non-zero) unless there
is an Prior Object ID Gap extension header (see Section 11.8).
{
Object ID Delta (vi64),
[Properties (..),]
Object Payload Length (vi64),
[Object Status (vi64),]
[Object Payload (..),]
}
Figure 25: MOQT Subgroup Object Fields
10.4.3. Closing Subgroup Streams
Subscribers will often need to know if they have received all objects
in a Subgroup, particularly if they serve as a relay or cache. QUIC
and Webtransport streams provide signals that can be used for this
purpose. Closing Subgroups promptly frees system resources and often
unlocks flow control credit to open more streams.
If a sender has delivered all objects in a Subgroup to the QUIC
stream, except any Objects with Locations smaller than the
subscription's Start Location, it MUST close the stream with a FIN.
If a sender closes the stream before delivering all such objects to
the QUIC stream, it MUST use a RESET_STREAM or RESET_STREAM_AT
[I-D.draft-ietf-quic-reliable-stream-reset] frame. This includes,
but is not limited to:
* An Object in an open Subgroup exceeding its Delivery Timeout
* Early termination of subscription due to request cancellation
Nandakumar, et al. Expires 3 September 2026 [Page 87]
Internet-Draft moq-transport March 2026
* A publisher's decision to end the subscription early
* A REQUEST_UPDATE moving the subscription's End Group to a smaller
Group or the Start Location to a larger Location
* Omitting a Subgroup Object due to the subscriber's Forward State
When RESET_STREAM_AT is used, the reliable_size SHOULD include the
stream header so the receiver can identify the corresponding
subscription and accurately account for reset data streams when
handling PUBLISH_DONE (see Section 9.13). Publishers that reset data
streams without using RESET_STREAM_AT with an appropriate
reliable_size can cause subscribers to hold on to subscription state
until a timeout expires.
A sender might send all objects in a Subgroup and the FIN on a QUIC
stream, and then reset the stream. In this case, the receiving
application would receive the FIN if and only if all objects were
received. If the application receives all data on the stream and the
FIN, it can ignore any RESET_STREAM it receives.
If a sender will not deliver any objects from a Subgroup, it MAY send
a SUBGROUP_HEADER on a new stream, with no objects, and then send
RESET_STREAM_AT with a reliable_size equal to the length of the
stream header. This explicitly tells the receiver there is an unsent
Subgroup.
A relay MUST NOT forward an Object on an existing Subgroup stream
unless it is the next Object in that Subgroup. A relay determines
that an Object is the next Object in the Subgroup if at least one of
the following is true:
* The Object ID is one greater than the previous Object sent on this
Subgroup stream.
* The Object was received on the same upstream Subgroup stream as
the previously sent Object on the downstream Subgroup stream, with
no other Objects in between.
* It determined all Object IDs between the current and previous
Object IDs on the Subgroup stream belong to different Subgroups or
do not exist.
If the relay does not know if an Object is the next Object, it MUST
reset the Subgroup stream and open a new one to forward it.
Nandakumar, et al. Expires 3 September 2026 [Page 88]
Internet-Draft moq-transport March 2026
Since SUBSCRIBEs always end on a group boundary, an ending
subscription can always cleanly close all its subgroups. A sender
that terminates a stream early for any other reason (e.g., to handoff
to a different sender) MUST use RESET_STREAM or RESET_STREAM_AT.
Senders SHOULD terminate a stream on Group boundaries to avoid doing
so.
An MOQT implementation that processes a stream FIN is assured it has
received all objects in a subgroup from the start of the
subscription. If a relay, it can forward stream FINs to its own
subscribers once those objects have been sent. A relay MAY treat
receipt of EndOfGroup or EndOfTrack objects as a signal to close
corresponding streams even if the FIN has not arrived, as further
objects on the stream would be a protocol violation.
Similarly, an EndOfGroup message indicates the maximum Object ID in
the Group, so if all Objects in the Group have been received, a FIN
can be sent on any stream where the entire subgroup has been sent.
This might be complex to implement.
Processing a RESET_STREAM or RESET_STREAM_AT means that there might
be other objects in the Subgroup beyond the last one received. A
relay might immediately reset the corresponding downstream stream, or
it might attempt to recover the missing Objects in an effort to send
all the Objects in the subgroups and the FIN. It also might send
RESET_STREAM_AT with reliable_size set to the last Object it has, so
as to reliably deliver the Objects it has while signaling that other
Objects might exist.
A subscriber MAY send a QUIC STOP_SENDING frame for a subgroup stream
if the Group or Subgroup is no longer of interest to it. The
publisher SHOULD respond with RESET_STREAM or RESET_STREAM_AT. If
RESET_STREAM_AT is sent, note that the receiver has indicated no
interest in the objects, so setting a reliable_size beyond the stream
header is of questionable utility.
RESET_STREAM and STOP_SENDING on SUBSCRIBE data streams have no
impact on other Subgroups in the Group or the subscription, although
applications might cancel all Subgroups in a Group at once.
A publisher that receives a STOP_SENDING on a Subgroup stream SHOULD
NOT attempt to open a new stream to deliver additional Objects in
that Subgroup.
The application SHOULD use a relevant error code in RESET_STREAM or
RESET_STREAM_AT, as defined below:
INTERNAL_ERROR (0x0): An implementation specific error.
Nandakumar, et al. Expires 3 September 2026 [Page 89]
Internet-Draft moq-transport March 2026
CANCELLED (0x1): The subscriber or publisher cancelled the Request.
For Subscriptions, PUBLISH_DONE (Section 9.13) will have a more
detailed status code.
DELIVERY_TIMEOUT (0x2): The DELIVERY TIMEOUT Section 9.3.3 was
exceeded for this stream.
SESSION_CLOSED (0x3): The publisher session is being closed.
UNKNOWN_OBJECT_STATUS (0x4): In response to a FETCH, the publisher
is unable to determine the Status of the next Object in the
requested range.
TOO_FAR_BEHIND (0x5): The corresponding subscription has exceeded
the publisher's resource limits and is being terminated (see
Section 9.3.3).
EXCESSIVE_LOAD (0x9): The publisher is overloaded and is resetting
this stream.
MALFORMED_TRACK (0x12): A relay publisher detected that the track
was malformed (see Section 2.4.2).
10.4.4. Fetch Header
When a stream begins with FETCH_HEADER, all objects on the stream
belong to the track requested in the Fetch message identified by
Request ID.
FETCH_HEADER {
Type (vi64) = 0x5,
Request ID (vi64),
}
Figure 26: MOQT FETCH_HEADER
Each Object sent on a FETCH stream after the FETCH_HEADER has the
following format:
Nandakumar, et al. Expires 3 September 2026 [Page 90]
Internet-Draft moq-transport March 2026
{
Serialization Flags (vi64),
[Group ID (vi64),]
[Subgroup ID (vi64),]
[Object ID (vi64),]
[Publisher Priority (8),]
[Properties (..),]
Object Payload Length (vi64),
[Object Payload (..),]
}
Figure 27: MOQT Fetch Object Fields
The Serialization Flags field defines the serialization of the
Object. It is a variable-length integer. When less than 128, the
bits represent flags described below. The following additional
values are defined:
+=======+===========================+
| Value | Meaning |
+=======+===========================+
| 0x8C | End of Non-Existent Range |
+-------+---------------------------+
| 0x10C | End of Unknown Range |
+-------+---------------------------+
Table 6
Any other value is a PROTOCOL_VIOLATION.
10.4.4.1. Flags
The two least significant bits (LSBs) of the Serialization Flags form
a two-bit field that defines the encoding of the Subgroup. To
extract this value, the Subscriber performs a bitwise AND operation
with the mask 0x03.
Nandakumar, et al. Expires 3 September 2026 [Page 91]
Internet-Draft moq-transport March 2026
+==============================+===============================+
| Bitmask Result | Meaning |
| (Serialization Flags & 0x03) | |
+==============================+===============================+
| 0x00 | Subgroup ID is zero |
+------------------------------+-------------------------------+
| 0x01 | Subgroup ID is the prior |
| | Object's Subgroup ID |
+------------------------------+-------------------------------+
| 0x02 | Subgroup ID is the prior |
| | Object's Subgroup ID plus one |
+------------------------------+-------------------------------+
| 0x03 | The Subgroup ID field is |
| | present |
+------------------------------+-------------------------------+
Table 7
The following table defines additional flags within the Serialization
Flags field. Each flag is an independent boolean value, where a set
bit (1) indicates the corresponding condition is true.
+=========+==========================+=========================+
| Bitmask | Condition if set | Condition if not set |
| | | (0) |
+=========+==========================+=========================+
| 0x04 | Object ID field is | Object ID is the prior |
| | present | Object's ID plus one |
+---------+--------------------------+-------------------------+
| 0x08 | Group ID field is | Group ID is the prior |
| | present | Object's Group ID |
+---------+--------------------------+-------------------------+
| 0x10 | Priority field is | Priority is the prior |
| | present | Object's Priority |
+---------+--------------------------+-------------------------+
| 0x20 | Properties field is | Properties field is not |
| | present | present |
+---------+--------------------------+-------------------------+
| 0x40 | Datagram: ignore the two | Decode the Subgroup ID |
| | least significant bits | as indicated by the two |
| | | least significant bits |
+---------+--------------------------+-------------------------+
Table 8
If the first Object in the FETCH response uses a flag that references
fields in the prior Object, the Subscriber MUST close the session
with a PROTOCOL_VIOLATION.
Nandakumar, et al. Expires 3 September 2026 [Page 92]
Internet-Draft moq-transport March 2026
The Object Properties structure is defined in Section 10.2.1.2.
When encoding an Object with a Forwarding Preference of "Datagram"
(see Section 10.2.1.2), the object has no Subgroup ID. The publisher
MUST SET bit 0x40 to '1'. When 0x40 is set, it SHOULD set the two
least significant bits to zero and the subscriber MUST ignore the
bits.
10.4.4.2. End of Range
When Serialization Flags indicates an End of Range (e.g. values 0x8C
or 0x10C), the Group ID and Object ID fields are present. Subgroup
ID, Priority and Properties are not present. All Objects with
Locations between the last serialized Object, if any, and this
Location, inclusive, either do not exist (when Serialization Flags is
0x8C) or are unknown (0x10C). A publisher SHOULD NOT use End of Non-
Existent Range in a FETCH response except to split a range of Objects
that will not be serialized into those that are known not to exist
and those with unknown status.
When an Object follows an End of Range indicator and uses flags that
reference the "prior Object", the prior Object fields are determined
as follows:
* Prior Group ID and prior Object ID: The values from the End of
Range indicator.
* Prior Subgroup ID: The Subgroup ID from the last actual Object
before the End of Range indicator. If there was no prior Object,
using a flag that references the prior Subgroup ID is a
PROTOCOL_VIOLATION.
* Prior Priority: The Priority from the last actual Object before
the End of Range indicator. If there was no prior Object, using a
flag that references the prior Priority is a PROTOCOL_VIOLATION.
10.5. Examples
Sending a subgroup on one stream:
Nandakumar, et al. Expires 3 September 2026 [Page 93]
Internet-Draft moq-transport March 2026
Stream = 2
SUBGROUP_HEADER {
Type = 0x14
Track Alias = 2
Group ID = 0
Subgroup ID = 0
Priority = 0
}
{
Object ID = 0
Object Payload Length = 4
Payload = "abcd"
}
{
Object ID = 1
Object Payload Length = 4
Payload = "efgh"
}
Sending a group on one stream, with the first object containing two
Properties.
Nandakumar, et al. Expires 3 September 2026 [Page 94]
Internet-Draft moq-transport March 2026
Stream = 2
SUBGROUP_HEADER {
Type = 0x35
Track Alias = 2
Group ID = 0
Subgroup ID = 0
}
{
Object ID Delta = 0 (Object ID is 0)
Properties Length = 33
{ Type = 4
Value = 2186796243
},
{ Type = 77
Length = 21
Value = "traceID:123456"
}
Object Payload Length = 4
Payload = "abcd"
}
{
Object ID Delta = 0 (Object ID is 1)
Properties Length = 0
Object Payload Length = 4
Payload = "efgh"
}
11. MOQT Properties
The following Properties are defined in MOQT. Each Property
specifies whether it can be used with Tracks, Objects, or both.
Property types in ranges reserved for application-specific use
(0x38-0x3F, 0x3800-0x3FFF) are not defined by MOQT. See Section 2.5
for usage guidance.
11.1. DELIVERY TIMEOUT
DELIVERY TIMEOUT (Property Type 0x02) is a Track Property. It
expresses the publisher's DELIVERY_TIMEOUT for a Track (see
Section 9.3.3).
A DELIVERY_TIMEOUT value of 0 indicates no timeout; Objects do not
expire due to delivery timeout.
Nandakumar, et al. Expires 3 September 2026 [Page 95]
Internet-Draft moq-transport March 2026
If both the subscriber specifies a DELIVERY_TIMEOUT parameter and the
Track has a DELIVERY_TIMEOUT property, the endpoints use the min of
the two non-zero values for the subscription. If either value is 0,
the non-zero value is used. If both are 0, there is no delivery
timeout.
If unspecified, the subscriber's DELIVERY_TIMEOUT is used. If
neither endpoint specified a timeout, Objects do not time out.
11.2. MAX CACHE DURATION
MAX_CACHE_DURATION (Property Type 0x04) is a Track Property.
It is an integer expressing the number of milliseconds an Object can
be served from a cache. If present, the relay MUST NOT start
forwarding any individual Object received through this subscription
or fetch after the specified number of milliseconds has elapsed since
the beginning of the Object was received. This means Objects earlier
in a multi-object stream will expire earlier than Objects later in
the stream. Once Objects have expired from cache, their state
becomes unknown, and a relay that handles a downstream request that
includes those Objects re-requests them.
If MAX_CACHE_DURATION is not sent by the publisher, the Objects can
be cached until implementation constraints cause them to be evicted.
11.3. DEFAULT PUBLISHER PRIORITY
DEFAULT PUBLISHER PRIORITY (Property Type 0x0E) is a Track Property
that specifies the priority of a subscription relative to other
subscriptions in the same session. The value is from 0 to 255 and
lower numbers get higher priority. See Section 7. Priorities above
255 are invalid. Subgroups and Datagrams for this subscription
inherit this priority, unless they specifically override it.
If omitted, the Default Publisher Priority is 128.
11.4. DEFAULT PUBLISHER GROUP ORDER
DEFAULT_PUBLISHER_GROUP_ORDER (Property Type 0x22) is a Track
Property.
It is an enum indicating the publisher's preference for prioritizing
Objects from different groups within the same subscription (see
Section 7). The allowed values are Ascending (0x1) or Descending
(0x2). If an endpoint receives a value outside this range, it MUST
close the session with PROTOCOL_VIOLATION.
Nandakumar, et al. Expires 3 September 2026 [Page 96]
Internet-Draft moq-transport March 2026
If omitted, the publisher's preference is Ascending (0x1).
11.5. DYNAMIC GROUPS
DYNAMIC_GROUPS (Property Type 0x30) is a Track Property. The allowed
values are 0 or 1. When the value is 1, it indicates that the
subscriber can request the Original Publisher to start a new Group by
including the NEW_GROUP_REQUEST parameter in PUBLISH_OK or
REQUEST_UPDATE for this Track. If an endpoint receives a value
larger than 1, it MUST close the session with PROTOCOL_VIOLATION.
If omitted, the value is 0.
11.6. Immutable Properties
Immutable Properties (Property Type 0xB) contain a sequence of Key-
Value-Pairs (see Figure 2) which are also Track or Object Properties.
Immutable Extensions {
Type (0xB),
Length (vi64),
Key-Value-Pair (..) ...
}
This Property can be added by the Original Publisher, but MUST NOT be
added by Relays. This Property MUST NOT be modified or removed and
the serialization (e.g. variable-length integer encodings) of the
Key-Value-Pairs MUST NOT change). Like other Properties, Relays MUST
cache Immutable Properties if the Object or Track are cached and MUST
forward it. Relays MAY decode and view the Properties in the Key-
Value-Pairs.
Unless specified by a particular Property specification, Properties
MAY appear either in the mutable extension list or inside Immutable
Properties. When looking for the value of a property, processors
MUST search both the mutable properties and the contents of Immutable
Extensions.
If a Property allows multiple values, the same Property Type MAY
appear in both the mutable list and inside Immutable Extensions,
unless prohibited by the Property specification.
A Track is considered malformed (see Section 2.4.2) if any of the
following conditions are detected:
* An Object contains an Immutable Properties property that contains
another Immutable Properties key.
Nandakumar, et al. Expires 3 September 2026 [Page 97]
Internet-Draft moq-transport March 2026
* A Key-Value-Pair cannot be parsed.
The following figure shows an example Object structure with a
combination of mutable and immutable properties and end to end
encrypted metadata in the Object payload.
Object Header Object Payload
<------------------------------------------------> <------------------->
+--------+-------+------------+-------+-----------+--------------------+
| Object | Ext 1 | Immutable | Ext N | [Payload] | Private Properties |
| Fields | | Properties | | [Length] | App Payload |
+--------+-------+------------+-------+-----------+--------------------+
xxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxx
yyyyyyyyyyyyyyyyyyyy
x = e2e Authenticated Data
y = e2e Encrypted Data
EXT 1 and EXT N can be modified or removed by Relays
An Object MUST NOT contain more than one instance of this property.
11.7. Prior Group ID Gap
Prior Group ID Gap only applies to Objects, not Tracks.
Prior Group ID Gap (Property Type 0x3C) is a variable length integer
containing the number of Groups prior to the current Group that do
not and will never exist. For example, if the Original Publisher is
publishing an Object in Group 7 and knows it will never publish any
Objects in Group 8 or Group 9, it can include Prior Group ID Gap = 2
in any number of Objects in Group 10, as it sees fit. A Track is
considered malformed (see Section 2.4.2) if any of the following
conditions are detected:
* An Object contains more than one instance of Prior Group ID Gap.
* A Group contains more than one Object with different values for
Prior Group ID Gap.
* An Object has a Prior Group ID Gap larger than the Group ID.
* An endpoint receives an Object with a Prior Group ID Gap covering
an Object it previously received.
* An endpoint receives an Object with a Group ID within a previously
communicated gap.
Nandakumar, et al. Expires 3 September 2026 [Page 98]
Internet-Draft moq-transport March 2026
Use of this property is optional, as publishers might not know the
prior gap size, or there may not be a gap. If Prior Group ID Gap is
not present, the receiver cannot infer any information about the
existence of prior groups (see Section 2.3.1).
This property can be added by the Original Publisher, but MUST NOT be
added by relays. This property MAY be removed by a relay when the
object in question is served via FETCH, and the gap that the
extension communicates is already communicated implicitly in the
FETCH response; it MUST NOT be modified or removed otherwise.
An Object MUST NOT contain more than one instance of this property.
11.8. Prior Object ID Gap
Prior Object ID Gap only applies to Objects, not Tracks.
Prior Object ID Gap (Property Type 0x3E) is a variable length integer
containing the number of Objects prior to the current Object that do
not and will never exist. For example, if the Original Publisher is
publishing Object 10 in Group 3 and knows it will never publish
Objects 8 or 9 in this Group, it can include Prior Object ID Gap = 2.
A Track is considered malformed (see Section 2.4.2) if any of the
following conditions are detected:
* An Object contains more than one instance of Prior Object ID Gap.
* An Object has a Prior Object ID Gap larger than the Object ID.
* An endpoint receives an Object with a Prior Object ID Gap covering
an Object it previously received.
* An endpoint receives an Object with an Object ID within a
previously communicated gap.
Use of this property is optional, as publishers might not know the
prior gap size, or there might not be a gap. If Prior Object ID Gap
is not present, the receiver cannot infer any information about the
existence of prior objects (see Section 2.1).
This property can be added by the Original Publisher, but MUST NOT be
added by relays. This property MAY be removed by a relay when the
object in question is served via FETCH, and the gap that the
extension communicates is already communicated implicitly in the
FETCH response; it MUST NOT be modified or removed otherwise.
An Object MUST NOT contain more than one instance of this property.
Nandakumar, et al. Expires 3 September 2026 [Page 99]
Internet-Draft moq-transport March 2026
12. Security Considerations
TODO: Expand this section, including subscriptions.
TODO: Describe Cache Poisoning attacks
12.1. Resource Exhaustion
Live content requires significant bandwidth and resources. Failure
to set limits will quickly cause resource exhaustion.
MOQT uses stream limits and flow control to impose resource limits at
the network layer. Endpoints SHOULD set flow control limits based on
the anticipated bitrate.
Endpoints MAY impose a MAX STREAM count limit which would restrict
the number of concurrent streams which an application could have in
flight.
The publisher prioritizes and transmits streams out of order.
Streams might be starved indefinitely during congestion. The
publisher and subscriber MUST cancel a stream, preferably the one
with the lowest priority, after reaching a resource limit.
12.2. Timeouts
Implementations are advised to use timeouts to prevent resource
exhaustion attacks by a peer that does not send expected data within
an expected time. Each implementation is expected to set its own
timeouts.
12.2.1. Idle Connection Handling
The transport connection (e.g., QUIC) underlying a MOQT session can
close due to idle timeout if no data is exchanged, either because
there are no established subscriptions or the established
subscriptions are not publishing Objects frequently. This includes
publisher sessions that have issued a PUBLISH_NAMESPACE and are
waiting for subscribers.
Implementations that want to keep idle sessions open have several
options:
* Use transport-layer keep-alive mechanisms, such as QUIC PING
frames, to prevent idle timeout closure.
* Send periodic control messages, for example REQUEST_UPDATE with no
modified Message Parameters.
Nandakumar, et al. Expires 3 September 2026 [Page 100]
Internet-Draft moq-transport March 2026
* Accept that idle connections can close and implement reconnection
logic when needed.
The choice of mechanism is implementation-specific.
12.3. Relay security considerations
12.3.1. State maintenance
A Relay SHOULD have mechanisms to prevent malicious endpoints from
flooding it with PUBLISH_NAMESPACE or SUBSCRIBE_NAMESPACE requests
that could bloat data structures. It could use QUIC stream limits to
limit the number of such requests, or could have application-specific
policies that can reject incoming PUBLISH_NAMESPACE or
SUBSCRIBE_NAMESPACE requests that cause the state maintenance for the
session to be excessive.
12.3.2. SUBSCRIBE_NAMESPACE with short prefixes
A Relay can use authorization rules in order to prevent subscriptions
closer to the root of a large prefix tree. Otherwise, if an entity
sends a relay a SUBSCRIBE_NAMESPACE message with a short prefix, it
can cause the relay to send a large volume of NAMESPACE messages. As
changes occur in the tree of namespaces, the relay would have to send
matching NAMESPACE/NAMESPACE_DONE messages.
12.4. Implementation Identification Fingerprinting
The MOQT_IMPLEMENTATION option (Section 9.4.1.5) can reveal
information that contributes to fingerprinting, a set of techniques
for identifying a specific endpoint over time through its unique set
of characteristics.
Detailed implementation information, including specific version
numbers, build identifiers, or platform details, can create a unique
fingerprint that enables tracking endpoints across sessions without
their awareness. When combined with other session characteristics,
even minimal implementation identification can contribute to
distinguishing one endpoint from another.
To mitigate fingerprinting risks:
* Implementations SHOULD send only the minimum information necessary
for interoperability debugging. A short implementation name and
major version number are typically sufficient.
Nandakumar, et al. Expires 3 September 2026 [Page 101]
Internet-Draft moq-transport March 2026
* Implementations SHOULD NOT include detailed system information,
build numbers, or other attributes that could uniquely identify a
specific instance or user.
* Privacy-conscious deployments MAY omit the MOQT_IMPLEMENTATION
option entirely or send a generic value.
* Implementations MAY provide users with the ability to configure or
disable the MOQT_IMPLEMENTATION option.
Operators should be aware that detailed implementation identification
facilitates the same privacy concerns as persistent identifiers,
since it enables correlation of sessions across time.
13. Grease
To ensure that implementations correctly handle unknown values and do
not fail when encountering protocol extensions they do not
understand, this document reserves a range of values for the purpose
of greasing; see Section 3.3 of [RFC9170].
Grease values follow the pattern 0x7f * N + 0x9D for non-negative
integer values of N (that is, 0x9D, 0xBC, ..., 0x3ffffffffffffffe).
The following registries include GREASE reservations:
* Setup Options (Section 9.4.1)
* Properties (Section 14.4)
* Session Termination Error Codes (Section 14.5.1)
* REQUEST_ERROR Codes (Section 14.5.2)
* PUBLISH_DONE Codes (Section 14.5.3)
* Data Stream Reset Error Codes (Section 14.5.4)
* MOQT Auth Token Type
Implementations MUST handle unknown values from these registries
gracefully according to the rules defined in each section.
Setup Options with reserved identifiers have no semantics and can
carry arbitrary values. Endpoints MUST ignore unknown Setup Options
as specified in Section 9.4.
Nandakumar, et al. Expires 3 September 2026 [Page 102]
Internet-Draft moq-transport March 2026
14. IANA Considerations
TODO: fill out currently missing registries:
* MOQT ALPN values
* Setup Options
* Message types
TODO: register the URI scheme and the ALPN
14.1. Authorization Token Alias Type
+======+===========+===============+
| Code | Name | Specification |
+======+===========+===============+
| 0x0 | DELETE | Section 9.3.2 |
+------+-----------+---------------+
| 0x1 | REGISTER | Section 9.3.2 |
+------+-----------+---------------+
| 0x2 | USE_ALIAS | Section 9.3.2 |
+------+-----------+---------------+
| 0x3 | USE_VALUE | Section 9.3.2 |
+------+-----------+---------------+
Table 9
14.2. MOQT Auth Token Type
+=================+=======================+===============+
| Code | Name | Specification |
+=================+=======================+===============+
| 0x0 | Reserved | Section 9.3.2 |
+-----------------+-----------------------+---------------+
| 0x7f * N + 0x9D | Reserved for greasing | Section 13 |
+-----------------+-----------------------+---------------+
Table 10
14.3. Message Parameters
+================+=====================+================+
| Parameter Type | Parameter Name | Specification |
+================+=====================+================+
| 0x02 | DELIVERY_TIMEOUT | Section 9.3.3 |
+----------------+---------------------+----------------+
| 0x03 | AUTHORIZATION_TOKEN | Section 9.3.2 |
Nandakumar, et al. Expires 3 September 2026 [Page 103]
Internet-Draft moq-transport March 2026
+----------------+---------------------+----------------+
| 0x04 | RENDEZVOUS_TIMEOUT | Section 9.3.4 |
+----------------+---------------------+----------------+
| 0x08 | EXPIRES | Section 9.3.8 |
+----------------+---------------------+----------------+
| 0x09 | LARGEST_OBJECT | Section 9.3.9 |
+----------------+---------------------+----------------+
| 0x10 | FORWARD | Section 9.3.10 |
+----------------+---------------------+----------------+
| 0x20 | SUBSCRIBER_PRIORITY | Section 9.3.5 |
+----------------+---------------------+----------------+
| 0x21 | SUBSCRIPTION_FILTER | Section 9.3.7 |
+----------------+---------------------+----------------+
| 0x22 | GROUP_ORDER | Section 9.3.6 |
+----------------+---------------------+----------------+
| 0x32 | NEW_GROUP_REQUEST | Section 9.3.11 |
+----------------+---------------------+----------------+
Table 11
* Message Parameters - List which params can be repeated in the
table.
14.4. Properties
+==========+===============================+========+===============+
| Type | Name | Scope | Specification |
+==========+===============================+========+===============+
| 0x02 | DELIVERY_TIMEOUT | Track | Section 11.1 |
+----------+-------------------------------+--------+---------------+
| 0x04 | MAX_CACHE_DURATION | Track | Section 11.2 |
+----------+-------------------------------+--------+---------------+
| 0x0B | IMMUTABLE_PROPERTIES | Track, | Section 11.6 |
| | | Object | |
+----------+-------------------------------+--------+---------------+
| 0x0E | DEFAULT_PUBLISHER_PRIORITY | Track | Section 11.3 |
+----------+-------------------------------+--------+---------------+
| 0x22 | DEFAULT_PUBLISHER_GROUP_ORDER | Track | Section 11.4 |
+----------+-------------------------------+--------+---------------+
| 0x30 | DYNAMIC_GROUPS | Track | Section 11.5 |
+----------+-------------------------------+--------+---------------+
| 0x3C | PRIOR_GROUP_ID_GAP | Object | Section 11.7 |
+----------+-------------------------------+--------+---------------+
| 0x3E | PRIOR_OBJECT_ID_GAP | Object | Section 11.8 |
+----------+-------------------------------+--------+---------------+
| 0x7f | Reserved for greasing | Any | Section 13 |
| * N + | | | |
| 0x9D | | | |
Nandakumar, et al. Expires 3 September 2026 [Page 104]
Internet-Draft moq-transport March 2026
+----------+-------------------------------+--------+---------------+
Table 12
Endpoints MUST ignore unknown Property types, skipping them using the
length field.
* MOQ Properties - we wish to define the following registration
policies:
- 0x00 to 0x37: Standards Action or IESG Approval (1-byte
encoding)
- 0x38 to 0x3F: Reserved for application-specific use (1-byte
encoding, no registration permitted)
- 0x40 to 0x37FF: Specification Required (2-byte encoding)
- 0x3800 to 0x3FFF: Reserved for application-specific use (2-byte
encoding, no registration permitted)
- 0x4000 and above: First Come First Served
Code points reserved for application-specific use will never be
allocated by IANA. Applications using these values do not need to
coordinate with IANA. Note that applications consuming tracks
from uncoordinated sources may encounter different semantics for
the same code points, creating potential collision risks.
14.5. Error Codes
14.5.1. Session Termination Error Codes
+=============================+=================+===============+
| Name | Code | Specification |
+=============================+=================+===============+
| NO_ERROR | 0x0 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| INTERNAL_ERROR | 0x1 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| UNAUTHORIZED | 0x2 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| PROTOCOL_VIOLATION | 0x3 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| INVALID_REQUEST_ID | 0x4 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| DUPLICATE_TRACK_ALIAS | 0x5 | Section 3.5 |
+-----------------------------+-----------------+---------------+
Nandakumar, et al. Expires 3 September 2026 [Page 105]
Internet-Draft moq-transport March 2026
| KEY_VALUE_FORMATTING_ERROR | 0x6 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| INVALID_REQUIRED_REQUEST_ID | 0x7 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| INVALID_PATH | 0x8 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| MALFORMED_PATH | 0x9 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| GOAWAY_TIMEOUT | 0x10 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| CONTROL_MESSAGE_TIMEOUT | 0x11 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| DATA_STREAM_TIMEOUT | 0x12 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| AUTH_TOKEN_CACHE_OVERFLOW | 0x13 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| DUPLICATE_AUTH_TOKEN_ALIAS | 0x14 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| VERSION_NEGOTIATION_FAILED | 0x15 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| MALFORMED_AUTH_TOKEN | 0x16 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| UNKNOWN_AUTH_TOKEN_ALIAS | 0x17 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| EXPIRED_AUTH_TOKEN | 0x18 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| INVALID_AUTHORITY | 0x19 | Section 3.5 |
+-----------------------------+-----------------+---------------+
| MALFORMED_AUTHORITY | 0x1A | Section 3.5 |
+-----------------------------+-----------------+---------------+
| Reserved for greasing | 0x7f * N + 0x9D | Section 13 |
+-----------------------------+-----------------+---------------+
Table 13
14.5.2. REQUEST_ERROR Codes
+============================+=================+===============+
| Name | Code | Specification |
+============================+=================+===============+
| INTERNAL_ERROR | 0x0 | Section 9.7 |
+----------------------------+-----------------+---------------+
| UNAUTHORIZED | 0x1 | Section 9.7 |
+----------------------------+-----------------+---------------+
| TIMEOUT | 0x2 | Section 9.7 |
+----------------------------+-----------------+---------------+
| NOT_SUPPORTED | 0x3 | Section 9.7 |
+----------------------------+-----------------+---------------+
Nandakumar, et al. Expires 3 September 2026 [Page 106]
Internet-Draft moq-transport March 2026
| MALFORMED_AUTH_TOKEN | 0x4 | Section 9.7 |
+----------------------------+-----------------+---------------+
| EXPIRED_AUTH_TOKEN | 0x5 | Section 9.7 |
+----------------------------+-----------------+---------------+
| GOING_AWAY | 0x6 | Section 9.7 |
+----------------------------+-----------------+---------------+
| EXCESSIVE_LOAD | 0x9 | Section 9.7 |
+----------------------------+-----------------+---------------+
| DOES_NOT_EXIST | 0x10 | Section 9.7 |
+----------------------------+-----------------+---------------+
| INVALID_RANGE | 0x11 | Section 9.7 |
+----------------------------+-----------------+---------------+
| MALFORMED_TRACK | 0x12 | Section 9.7 |
+----------------------------+-----------------+---------------+
| DUPLICATE_SUBSCRIPTION | 0x19 | Section 9.7 |
+----------------------------+-----------------+---------------+
| UNINTERESTED | 0x20 | Section 9.7 |
+----------------------------+-----------------+---------------+
| PREFIX_OVERLAP | 0x30 | Section 9.7 |
+----------------------------+-----------------+---------------+
| NAMESPACE_TOO_LARGE | 0x31 | Section 9.7 |
+----------------------------+-----------------+---------------+
| INVALID_JOINING_REQUEST_ID | 0x32 | Section 9.7 |
+----------------------------+-----------------+---------------+
| Reserved for greasing | 0x7f * N + 0x9D | Section 13 |
+----------------------------+-----------------+---------------+
Table 14
14.5.3. PUBLISH_DONE Codes
+=======================+=================+===============+
| Name | Code | Specification |
+=======================+=================+===============+
| INTERNAL_ERROR | 0x0 | Section 9.13 |
+-----------------------+-----------------+---------------+
| UNAUTHORIZED | 0x1 | Section 9.13 |
+-----------------------+-----------------+---------------+
| TRACK_ENDED | 0x2 | Section 9.13 |
+-----------------------+-----------------+---------------+
| SUBSCRIPTION_ENDED | 0x3 | Section 9.13 |
+-----------------------+-----------------+---------------+
| GOING_AWAY | 0x4 | Section 9.13 |
+-----------------------+-----------------+---------------+
| EXPIRED | 0x5 | Section 9.13 |
+-----------------------+-----------------+---------------+
| TOO_FAR_BEHIND | 0x6 | Section 9.13 |
+-----------------------+-----------------+---------------+
Nandakumar, et al. Expires 3 September 2026 [Page 107]
Internet-Draft moq-transport March 2026
| UPDATE_FAILED | 0x8 | Section 9.13 |
+-----------------------+-----------------+---------------+
| EXCESSIVE_LOAD | 0x9 | Section 9.13 |
+-----------------------+-----------------+---------------+
| MALFORMED_TRACK | 0x12 | Section 9.13 |
+-----------------------+-----------------+---------------+
| Reserved for greasing | 0x7f * N + 0x9D | Section 13 |
+-----------------------+-----------------+---------------+
Table 15
14.5.4. Data Stream Reset Error Codes
+=======================+=================+================+
| Name | Code | Specification |
+=======================+=================+================+
| INTERNAL_ERROR | 0x0 | Section 10.4.3 |
+-----------------------+-----------------+----------------+
| CANCELLED | 0x1 | Section 10.4.3 |
+-----------------------+-----------------+----------------+
| DELIVERY_TIMEOUT | 0x2 | Section 10.4.3 |
+-----------------------+-----------------+----------------+
| SESSION_CLOSED | 0x3 | Section 10.4.3 |
+-----------------------+-----------------+----------------+
| UNKNOWN_OBJECT_STATUS | 0x4 | Section 10.4.3 |
+-----------------------+-----------------+----------------+
| TOO_FAR_BEHIND | 0x5 | Section 10.4.3 |
+-----------------------+-----------------+----------------+
| EXCESSIVE_LOAD | 0x9 | Section 10.4.3 |
+-----------------------+-----------------+----------------+
| MALFORMED_TRACK | 0x12 | Section 10.4.3 |
+-----------------------+-----------------+----------------+
| Reserved for greasing | 0x7f * N + 0x9D | Section 13 |
+-----------------------+-----------------+----------------+
Table 16
Contributors
The original design behind this protocol was inspired by three
independent proposals: WARP [I-D.draft-lcurley-warp] by Luke Curley,
RUSH [I-D.draft-kpugin-rush] by Kirill Pugin, Nitin Garg, Alan
Frindell, Jordi Cenzano and Jake Weissman, and QUICR
[I-D.draft-jennings-moq-quicr-proto] by Cullen Jennings, Suhas
Nandakumar and Christian Huitema. The authors of those documents
merged their proposals to create the first draft of moq-transport.
The IETF MoQ Working Group received an enormous amount of support
from many people. The following people provided substantive
Nandakumar, et al. Expires 3 September 2026 [Page 108]
Internet-Draft moq-transport March 2026
contributions to this document:
* Ali Begen
* Charles Krasic
* Christian Huitema
* Cullen Jennings
* James Hurley
* Jordi Cenzano
* Kirill Pugin
* Luke Curley
* Martin Duke
* Mike English
* Mo Zanaty
* Will Law
Use of Generative AI
Anthropic's Claude was used to assist with drafting and editing text
for this document. All AI-generated content was reviewed and
approved by the editors.
References
Normative References
[I-D.draft-ietf-quic-reliable-stream-reset]
Seemann, M. and K. Oku, "QUIC Stream Resets with Partial
Delivery", Work in Progress, Internet-Draft, draft-ietf-
quic-reliable-stream-reset-07, 14 June 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
reliable-stream-reset-07>.
[QUIC] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.
Nandakumar, et al. Expires 3 September 2026 [Page 109]
Internet-Draft moq-transport March 2026
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/rfc/rfc3629>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/rfc/rfc3986>.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/rfc/rfc7301>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers
(URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
<https://www.rfc-editor.org/rfc/rfc8615>.
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
[RFC9221] Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
Datagram Extension to QUIC", RFC 9221,
DOI 10.17487/RFC9221, March 2022,
<https://www.rfc-editor.org/rfc/rfc9221>.
[WebTransport]
Frindell, A., Kinnear, E., and V. Vasiliev, "WebTransport
over HTTP/3", Work in Progress, Internet-Draft, draft-
ietf-webtrans-http3-14, 20 October 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-
webtrans-http3-14>.
Informative References
Nandakumar, et al. Expires 3 September 2026 [Page 110]
Internet-Draft moq-transport March 2026
[I-D.draft-jennings-moq-quicr-proto]
Jennings, C. F., Nandakumar, S., and C. Huitema, "QuicR -
Media Delivery Protocol over QUIC", Work in Progress,
Internet-Draft, draft-jennings-moq-quicr-proto-01, 11 July
2022, <https://datatracker.ietf.org/doc/html/draft-
jennings-moq-quicr-proto-01>.
[I-D.draft-kpugin-rush]
Pugin, K., Garg, N., Frindell, A., Ferret, J. C., and J.
Weissman, "RUSH - Reliable (unreliable) streaming
protocol", Work in Progress, Internet-Draft, draft-kpugin-
rush-03, 21 April 2025,
<https://datatracker.ietf.org/doc/html/draft-kpugin-rush-
03>.
[I-D.draft-lcurley-warp]
Curley, L., Pugin, K., Nandakumar, S., and V. Vasiliev,
"Warp - Live Media Transport over QUIC", Work in Progress,
Internet-Draft, draft-lcurley-warp-04, 13 March 2023,
<https://datatracker.ietf.org/doc/html/draft-lcurley-warp-
04>.
[I-D.ietf-scone-protocol]
Thomson, M., Huitema, C., Oku, K., Joras, M., and L. M.
Ihlar, "Standard Communication with Network Elements
(SCONE) Protocol", Work in Progress, Internet-Draft,
draft-ietf-scone-protocol-04, 14 December 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-scone-
protocol-04>.
[I-D.ietf-webtrans-overview]
Kinnear, E. and V. Vasiliev, "The WebTransport Protocol
Framework", Work in Progress, Internet-Draft, draft-ietf-
webtrans-overview-11, 20 October 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-
webtrans-overview-11>.
[RFC6582] Henderson, T., Floyd, S., Gurtov, A., and Y. Nishida, "The
NewReno Modification to TCP's Fast Recovery Algorithm",
RFC 6582, DOI 10.17487/RFC6582, April 2012,
<https://www.rfc-editor.org/rfc/rfc6582>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.
Nandakumar, et al. Expires 3 September 2026 [Page 111]
Internet-Draft moq-transport March 2026
[RFC9170] Thomson, M. and T. Pauly, "Long-Term Viability of Protocol
Extension Mechanisms", RFC 9170, DOI 10.17487/RFC9170,
December 2021, <https://www.rfc-editor.org/rfc/rfc9170>.
[RFC9438] Xu, L., Ha, S., Rhee, I., Goel, V., and L. Eggert, Ed.,
"CUBIC for Fast and Long-Distance Networks", RFC 9438,
DOI 10.17487/RFC9438, August 2023,
<https://www.rfc-editor.org/rfc/rfc9438>.
Appendix A. Change Log
RFC Editor's Note: Please remove this section prior to publication of
a final version of this document.
Issue and pull request numbers are listed with a leading octothorp.
A.1. Since draft-ietf-moq-transport-16
*Session and Control Plane*
* Change control stream from bidi to a pair of uni streams (#1510)
* Collapse CLIENT_SETUP and SERVER_SETUP into a single SETUP message
(#1510)
* Move requests to bidirectional streams; remove cancel messages
(#1389)
* Remove MAX_REQUEST_ID/REQUESTS_BLOCKED (#1471)
* New variable-length integer encoding (#1016)
* Encode Message Parameters as Type-Value pairs (#1462)
* Add GREASE for Setup Options, Properties, and error code
registries (#1460)
* Add RENDEZVOUS_TIMEOUT parameter for SUBSCRIBE (#1447)
* Add PUBLISH_BLOCKED message for SUBSCRIBE_NAMESPACE flow control
(#1452)
* Add Timeout field to GOAWAY message (#1497)
* Add GOING_AWAY to REQUEST_ERROR codes (#1434)
* Add EXCESSIVE_LOAD error code (#1479)
Nandakumar, et al. Expires 3 September 2026 [Page 112]
Internet-Draft moq-transport March 2026
* Add NAMESPACE_TOO_LARGE error and stream reset for large
namespaces (#1496)
* Add TOO_FAR_BEHIND stream reset code (#1445)
* Add REQUEST_UPDATE to list of REQUEST_ERROR causes (#1466)
* Enforce REQUEST_OK/ERROR as first frame on the response stream
(#1499)
* Allow joining FETCH for PUBLISH and REQUEST_UPDATE with forward=1
(#1335)
* Allow DELIVERY_TIMEOUT value of 0 to mean no timeout (#1450)
* Allow zero-element namespaces (#1472)
* Clarify EXPIRES parameter update mechanism (#1448)
* Remove TRACK_STATUS from REQUEST_UPDATE (#1436)
* Define how to use auth token cache safely with multiple streams
(#1430)
* Constrain encoding/parsing of track namespace and names (#1512)
* Reserve Property type ranges for application-specific use (#1473)
* Make EndGroup in Subscription Filters a delta (#1470)
* Copy DELIVERY_TIMEOUT min requirement from parameter to property
(#1427)
*Data Plane Wire Format and Handling*
* Clarify prior Object semantics after End of Range indicators in
FETCH (#1513)
* Clarify datagram status and properties cases (#1444)
* Clarify Stream Count includes empty subgroups (#1449)
* Clarify language for malformed tracks in a subgroup with
END_OF_GROUP (#1464)
* Properties can appear in mutable list or inside Immutable
Properties (#1442)
Nandakumar, et al. Expires 3 September 2026 [Page 113]
Internet-Draft moq-transport March 2026
* Clarify immutable property preservation requirements (#1441)
* Clarification for Track Alias uniqueness (#1418)
*Notable Editorial Changes*
* Rename Setup Parameters to Setup Options (#1461)
* Rename Extension Headers to Properties (#1504)
* Add security/privacy considerations for MOQT_IMPLEMENTATION
(#1511)
* Add editorial text on bandwidth probing techniques (#1477)
* Explain idle connection handling (#1443)
* Fix "SUBSCRIBE_NAMESPACE with short prefixes" (#1502)
* Add generative AI disclosure per IRTF guidelines
A.2. Since draft-ietf-moq-transport-15
*Setup and Control Plane*
* Delta encode Key-Value-Pairs for Parameters and Headers (#1315)
* Use Request ID in PUBLISH_NAMESPACE_{DONE/CANCEL} (#1329)
* Remove delivery related params from TRACK_STATUS for Subscribers
(#1325)
* PUBLISH does not imply PUBLISH_NAMESPACE (#1364)
* Allow Start Location to decrease in SUBSCRIBE_UPDATE (#1323)
* Change SUBSCRIBE_UPDATE to REQUEST_UPDATE and expand ability to
update (#1332)
* Put SUBSCRIBE_NAMESPACE on a stream, make Namespaces and PUBLISH
independent (#1344)
* Require NAMESPACE before NAMESPACE_DONE (#1392)
* Allow the '*' or the empty namespace in SUBSCRIBE_NAMESPACE
(#1393)
* Relays match SUBSCRIBE to both Tracks and Namespaces (#1397)
Nandakumar, et al. Expires 3 September 2026 [Page 114]
Internet-Draft moq-transport March 2026
* Clarify sending requests after sending GOAWAY (#1398)
* Add Retry Interval to REQUEST_ERROR (#1339)
* Add Extension Headers to PUBLISH, SUBSCRIBE_OK, and FETCH_OK
(#1374)
* Move track properties to extensions, scope parameters (#1390)
* Add LARGEST_OBJECT parameter to TRACK_STATUS (#1367)
* Duplicate subscription processing (#1341)
* Address Track Name/Namespace edge cases (#1399)
*Data Plane Wire Format and Handling*
* Enable mixing datagrams with streams in one track (#1350)
* Clarify datagrams and subgroups (#1382)
* Redo the way we deal with missing Objects and Object Status
(#1342)
* Allow unknown ranges in a FETCH response (#1331)
* Do not reopen subgroups after delivery timeout or STOP_SENDING
(#1396)
* Clarify handling of unknown extensions (#1395)
* Clarify Delivery Timeout for datagrams (#1406)
* Disallow DELIVERY_TIMEOUT=0 (#1330)
* Malformed track due to multiple priorities for one subgroup
(#1317)
*Notable Editorial Changes*
* Subscribers can migrate networks too (#1410)
* Rename Version Specific Parameters to Message Parameters (#1411)
* Clarify valid joining fetch subscription states (#1363)
* Formatting names for logs (#1355)
Nandakumar, et al. Expires 3 September 2026 [Page 115]
Internet-Draft moq-transport March 2026
* A Publisher might not use the congestion window (#1408)
A.3. Since draft-ietf-moq-transport-14
*Setup and Control Plane*
* Always use ALPN for version negotiation (#499)
* Consolidate all the Error Message types (#1159)
* Change MOQT IMPLEMENTATION code point to 0x7 (#1191)
* Add Forward to SUBSCRIBE_NAMESPACE (#1220)
* Parameters for Group Order, Subscribe Priority and Subscription
Filter (redo) (#1273)
* REQUEST_OK message (#1274)
* Subscribe Update Acknowledgements (#1275)
* Disallow DELETE and USE_ALIAS in CLIENT_SETUP (#1277)
* Remove Expires field from SUBSCRIBE_OK (#1282)
* Make Forward a Parameter (#1283)
* Allow SUBSCRIBE_UPDATE to increase the end location (#1288)
* Add default port for raw QUIC (#1289)
* Unsubscribe Namespace should be linked to Subscribe Namespace
(#1292)
*Data Plane Wire Format and Handling*
* Fetch Object serialization optimization (#949)
* Make default PUBLISHER PRIORITY a parameter, optional in Subgroup/
Datagram (#1056)
* Allow datagram status with object ID=0 (#1197)
* Disallow object extension headers in all non-Normal status objects
(#1266)
* Objects for malformed track must not be cached (#1290)
Nandakumar, et al. Expires 3 September 2026 [Page 116]
Internet-Draft moq-transport March 2026
* Remove NO_OBJECTS fetch error code (#1303)
* Clarify what happens when max_cache_duration parameter is omitted
(#1287)
*Notable Editorial Changes*
* Rename Request ID field in MAX_REQUEST_ID (#1250)
* Define and draw subscription state machine (#1296)
* Omitting a subgroup object necessitates reset (#1295)
* Define duplication rules for header extensions (#1293)
* Clarify joining fetch end location (#1286)
A.4. Since draft-ietf-moq-transport-13
*Setup and Control Plane*
* Add an AUTHORITY parameter (#1058)
* Add a free-form SETUP parameter identifying the implementation
(#1114)
* Add a Request ID to SUBSCRIBE_UDPATE (#1106)
* Indicate which params can appear PUBLISH* messages (#1071)
* Add TRACK_STATUS to the list of request types affected by GOAWAY
(#1105)
*Data Plane Wire Format and Handling*
* Delta encode Object IDs within Subgroups (#1042)
* Use a bit in Datagram Type to convey Object ID = 0 (#1055)
* Corrected missed code point updates to Object Datagram Status
(#1082)
* Merge OBJECT_DATAGRAM and OBJECT_DATAGRAM_STATUS description
(#1179)
* Objects are not schedulable if flow-control blocked (#1054)
* Clarify DELIVERY_TIMEOUT reordering computation (#1120)
Nandakumar, et al. Expires 3 September 2026 [Page 117]
Internet-Draft moq-transport March 2026
* Receiving unrequested Objects (#1112)
* Clarify End of Track (#1111)
* Malformed tracks apply to FETCH (#1083)
* Remove early FIN from the definition of malformed tracks (#1096)
* Prior Object ID Gap Extension header (#939)
* Add Extension containing immutable extensions (#1025)
*Relay Handling*
* Explain FETCH routing for relays (#1165)
* MUST for multi-publisher relay handling (#1115)
* Filters don't (usually) determine the end of subscription (#1113)
* Allow self-subscriptions (#1110)
* Explain Namespace Prefix Matching in more detail (#1116)
*Explanatory*
* Explain Modularity of MOQT (#1107)
* Explain how to resume publishing after losing state (#1087)
*Major Editorial Changes*
* Rename ANNOUNCE to PUBLISH_NAMESPACE (#1104)
* Rename SUBSCRIBE_DONE to PUBLISH_DONE (#1108)
* Major FETCH Reorganization (#1173)
* Reformat Error Codes (#1091)
A.5. Since draft-ietf-moq-transport-12
* TRACK_STATUS_REQUEST and TRACK_STATUS have changed to directly
mirror SUBSCRIBE/OK/ERROR (#1015)
* SUBSCRIBE_ANNOUNCES was renamed back to SUBSCRIBE_NAMESPACE
(#1049)
Nandakumar, et al. Expires 3 September 2026 [Page 118]
Internet-Draft moq-transport March 2026
A.6. Since draft-ietf-moq-transport-11
* Move Track Alias from SUBSCRIBE to SUBSCRIBE_OK (#977)
* Expand cases FETCH_OK returns Invalid Range (#946) and clarify
fields (#936)
* Add an error code to FETCH_ERROR when an Object status is unknown
(#825)
* Rename Latest Object to Largest Object (#1024) and clarify what to
do when it's incomplete (#937)
* Explain Malformed Tracks and what to do with them (#938)
* Allow End of Group to be indicated in a normal Object (#1011)
* Relays MUST have an upstream subscription to send SUBSCRIBE_OK
(#1017)
* Allow AUTHORIZATION TOKEN in CLIENT_SETUP, SERVER_SETUP and other
fixes (#1013)
* Add PUBLISH for publisher initiated subscriptions (#995) and fix
the PUBLISH codepoints (#1048, #1051)
A.7. Since draft-ietf-moq-transport-10
* Added Common Structure definitions - Location, Key-Value-Pair and
Reason Phrase
* Limit lengths of all variable length fields, including Track
Namespace and Name
* Control Message length is now 16 bits instead of variable length
* Subscribe ID became Request ID, and was added to most control
messages. Request ID is used to correlate OK/ERROR responses for
ANNOUNCE, SUBSCRIBE_NAMESPACE, and TRACK_STATUS. Like Subscribe
ID, Request IDs are flow controlled.
* Explain rules for caching in more detail
* Changed the SETUP parameter format for even number parameters to
match the Object Header Extension format
* Rotated SETUP code points
Nandakumar, et al. Expires 3 September 2026 [Page 119]
Internet-Draft moq-transport March 2026
* Added Parameters to TRACK_STATUS and TRACK_STATUS_REQUEST
* Clarified how subscribe filters work
* Added Next Group Filter to SUBSCRIBE
* Added Forward flag to SUBSCRIBE
* Renamed FETCH_OK field to End and clarified how to set it
* Added Absolute Joining Fetch
* Clarified No Error vs Invalid Range FETCH_ERROR cases
* Use bits in SUBGROUP_HEADER and DATAGRAM* types to compress
subgroup ID and extensions
* Coalesced END_OF_GROUP and END_OF_TRACK_AND_GROUP status
* Objects that Do Not Exist cannot have extensions when sent on the
wire
* Specified error codes for resetting data streams
* Defined an Object Header Extension for communicating a known Group
ID gap
* Replaced AUTHORIZATION_INFO with AUTHORIZATION_TOKEN, which has
more structure, compression, and additional Auth related error
codes (#760)
Authors' Addresses
Suhas Nandakumar
Cisco
Email: snandaku@cisco.com
Victor Vasiliev
Google
Email: vasilvv@google.com
Ian Swett (editor)
Google
Email: ianswett@google.com
Nandakumar, et al. Expires 3 September 2026 [Page 120]
Internet-Draft moq-transport March 2026
Alan Frindell (editor)
Meta
Email: afrind@meta.com
Nandakumar, et al. Expires 3 September 2026 [Page 121]